Imagens das páginas
PDF
ePub

fungus has a season of rest underground, and whether in the witnesses such losses, which are regarded with complete indiffercondition of resting spores, a sclerotioid mass or a number of my: ence by our local representatives of Science. It is unaccountable celioid threads, the principal fact remains that the fungus lives that not one of our provincial Societies has as yet had the public through the winter in a state of rest. As to certain potatoes spirit, energy, or foresight to see the importance of this work and being able to resist the disease, I shall shortly be able to show of raising a fund for the purpose of ultimately securing such colthat whilst certain breeds of potatoes entirely resist it in one lections for the district. place, they fall a ready prey to it in another.

It is a question of national scientific importance. The collecHence any experiments carried on in one place by one person, tions which are formed during the present century may be said though valuable in themselves, must be inconclusive and im to represent the “pick” of the country. By.and-by, when loperfect.

calities are worked out, and the rarity and value of specimens The great question is, “How can the disease be evaded or greatly increased, we may awaken to a sense of the mistake we destroyed ?" and this can only be answered, if answered at all, have made in not devoting our energies less to palæontological by men who thoroughly know the fungus and its allies.

literature, and more to the formation of complete and exhaustive WORTHINGTON G. SMITH local series and collections, and thus smoothing the path of, and

providing interest for, the investigators of our fossil and recent

flora and fauna. The Denudation of Limestone Hills of Sarawak

Such is the lack of originality displayed in this country, and There is an agency in the denudation of the limestone rocks precedent is so blindly followed, that everywhere we find narrow of Saràwak which I do not think has been noted, but which is scientific cliques, so-called “Societies," apparently formed merely very efficient locally in its operation.

for the sake of having social gatherings and by means of a local The limestone in question is a dark-blue compact rock (pro- i periodical facilitating the cheap publication of the papers of such bably the oldest stratified formation in this part of Borneo) full as contribute. of fissures and joints, and sorming hilly tracts in Sarawak proper 1 The energy thus expended is almost entirely thrown away. and Samarahan. It is a not uncommon occurrence during | Indeed, so far as the journals of these “societies” are periods of unusual drought for the jungle clothing these hills to concerned, these societies are mere hindrances to the progress take fire in some unascertained way, and for large tracts of the of Science, for, did they not exist, the papers which appear vegetation to be destroyed before the conflagration dies out or in their obscure journals (or “ napkins,” in which the “talents" is extinguished by rains. Such an accident took place two years of these societies lie hid) might be contributed to such as have ago on the Jambusan hill, and a short time previously on Gunong a general circulation, and thus benefit the world at large. I Añgus (whence the present name, “Burnt Hill”), and on Mara- would most earnestly impress on our scientific Societies the great jah, a large hill near Bidi; and I have been informed by natives importance of devoting their energies more to the formation that similar fires are known at the hcad of the Undup, where and preservation of complete and exhaustive local collections. I have observed from a distance extensive masses of limestone. ( With such division of labour how much more accurate and rapid

When such a fire takes place, not only may we take for granted would be the progress of the sciences of Geology and Biology. that a great deal of surface-rock is more or less calcined, so as

S. G. P. to be easily removable by the heavy tropical rains ; but, there being no covering of soil to speak of, and the exterior rock

The Killing of Entomological Specimens having been merely bound together by a matted network of roots and creepers, large masses of rock-long loosened by A NOTE in a recent number of NATURE, reminds me weathering, or freshly detached by the expansion of air and / of some experiments I made about 15 years ago upon the action water in the fissures-keep falling from the higher parts of the of the vapours of volatile liquids (hydrocarbons, chloroform, &c.) hill as their supports are burnt away ; whilst groups of burning on insects, my object being to find an expeditious and painless trees go crashing down the scarps, assisting the work of degra method of killing entomological specimens. Several vapours dation by collision with the inequalities in their paths.

produced insensibility from which the insects recovered more or It is, however, subsequently to the fire that its most impor less rapidly, but bisulphide of carbon vapour killed them effectant effects become apparent. For the next year or two fresh tually. dislodgments of rock will be continually taking place, particu

My method of applying it was to place a few layers of blotting larly when, after the almost daily rains, the sun shines out, paper, lint, or cotton wool, on the bottom of a wide-mouthed striking on the bared rock with rays of tropical fervour. Many bottle, pill box, or other convenient place of execution ; then to years elapse before sufficient soil collects in the crevices of the | pour a few drops of the liquid upon this and confine the insect rock to support vegetation; and until the whitened face of the in the receptacle, which on account of the great density of the hill is once more shrouded in jungle, it remains immediately ex vapour need not be very accurately closed. The action of the posed to steady sub-aërial denudation; so that, bearing in mind | vapour must be continued a few minutes after signs of life have the immense rainfall, the abundance of fissures and joints in the disappeared, or the insect will recover. stone, and its solubility, I am inclined to believe that the degra. The most obstinate of beetles succumb without a struggle, and dation of these hills which goes on during the interval before the most delicate of moths or butterflies are uninjured, provided they again become efficiently shielded with vegetation, is com

the liquid itself does not touch them. Butterflies may be killed parable to centuries of waste of the same rock under ordinary

after they are pinned out, by simply placing a little cotton wool conditions.

soaked with the bisulphide in a box near to them. Were the limestone hills of Sarawak more gently rounded and

W. MATTIEU WILLIAMS less scarped, their destruction throu h the agencies above de. scribed might not be noteworthy; but, owing to the frequency of lines of old sea-cliffs and mural precipices, nearly the whole

Lecture Experiments of the detached rock passes at once to the bases of the hills,

The result of convection in a liquid, tending to cause the where it is again attacked by the rains, assisted now by running

upper part of the mass to be constantly at a higher temperature streams or standing water.

than the lower, may be well illustrated by the two following Sarawak, July 1

A. HART EVERETT

experiments :

Two large glass beakers are placed in front of a sheet of white

raper, one of them filled with cold the other with boiling water. An Appeal to our Provincial Scientific Societies

A boiling-tube filled with freshly prepared starch solution which Now that our provincial museums are yearly increasing in has been coloured deep blue by gradual addition of aqueous number, it appears desirable to draw the attention of the pro | solution of iodine, and has then been heated until the colour just vincial scientific societies to their importance as the centres for | disappears, is plunged into the beaker of cold water ; the blue the private collections illustrative of the local geology, natural colour, caused to return by the cooling of the solution, will ap. history, and archäology which from time to time conie into the pear first at the bottom of the tube and then gradually creep market. We are entirely indebted to private energy for any upwards, showing that the lower part of the heated liquid first British collections which we possess. How lamentable then is becomes sufficiently cooled to cause the return of the colour. In it that there is no public system for centralising them in our order to insure the disappearance of this colour by heat, an public museums, and thus saving them from dispersion by their excess of iodine must be carefully avoided. passing into the hands of dealers or private collectors, or into the In the boiling water contained in the other beaker is immersed possession of foreign or metropolitan museums. Every year ( a boiling-tube filled with the blue liquid obtained by adding

fangs.

caustic soda in excess to a solution of copper sulphate and tar property was escaping, stepped gravely after the snake and laid taric acid, with which has been mixed a little grape sugar (a hold of it by the tail. As a natural consequence, round came small quantity of “set” honey): the formation of yellow cuprous the cobra and menaced the monkey, which, retreating with sunoxide commences at the surface of the liquid, and is seen gradu dry grimaces, took refuge with the juggler, in great alarm at the ally to extend to the lower parts, showing: hat the upper parts turn events had taken. first attain the temperature requisite to cause the reaction to This cobra is a small one, and as it is one of those very pale, occur which precipitates cuprous oxide.

almost cream-coloured varieties, that finds no mention in GuinThese experiments are easy of execution, and by the above ther's able work, I am anxious to examine it thoroughly. The arrangement, or still better by being projected on the screen, owner, however, affirms that he has to draw its fangs about once may be rendered visible at a considerable distance.

a month, and as he is most cautious in handling the reptile, it is Queenwood College

FRANK CLOWES | probable that the fang matrix has not been destroyed, and ex

amination will be safest just after the operation of extracting the Mr. Garrod's Theory of Nerve-Force

Mangalore, Sept. 12

E H. PRINGLE The thermo-electric theory of nerve-force propounded by Mr. Garrod (NATURE, vol. viii. p. 265) seems capable of extension. If a pole of metal, cased in a non-conducting sheath, were sunk in an artesian boring so as to reach from the level of constant temperature to the greatest depth attainable, how far would such

CLASSIFICATION OF CLOUDS* pole fulfil the conditions of a sheathed nerve penetrating from IN an essay on the “ Modifications of Clouds, read to the cool surlace of an animal to the warmer interior? And with

11 the Askesian Society in 1802, Howard first proposed so litile difference of temperature in so great a length, woult its his classification of clouds. which has since been the dynamic effect be at all appreciable? A quarter of a mile of submarine cable let down the shaft of

generally received authority on the subject. His system our Carnbrea mine might represent a sheathed nerve ; and any

has thus stood its ground for more than half a century, in existing nerve-force might there be tested. Abandoned mine

spite of its defects and of the misconstruction not unfreshafts are the terrors of our Cornish moorlands. Is it quently put on the two terms, “stratus” and “nimbus ” within the power of Science to convert them into earth-nerves, since the publication of Kaemtz's Meteorology. These say by lining their sides with non-conducting material, and then misapprehensions and the obscurity and confusion arising packing them tight with conductive slag or some kind of metallic from them are pointed out by Prof. Poey, but the errors refuse? And is it possible, even in theory, to make such earth. have not been followed so generally as is asserted, at least nerves work some kind of earth-muscle? For ignorant me to by British meteorologists. In a series of papers issued at speak of this subject is ultracrepidism (NATURE, vol. vii. p. 262). intervals during the past eleven years, Prof. Poey has enYet it seems a fair extension of Mr. Garrod's ingenious theory.

deavoured to develop a new classification of clouds, of

AUGUSTINE CHUDLEIGH Carnbrea, Cornwall

which the volume before us is the result.

The following is Poey's classification compared with

that of Howard :Genesis in Borneo

Pory's CLASSIFICATION. | Howard's ClassiFICATION. MR. CAMERON's paper read at the Society of Biblical Archæo

Cloud composed of First type : cirrus. logy, testifies to the early diffusion of Semitic traditions by the

(cirro-stratus.

First type : agency, it may be inserred, of Moslem converts.

cirrus spicules of Derived:

cirro-cumulus.

(cirro-stratus ice. The same traditional coincidences recorded of Borneo are

Second type : cumulus.
Derived : cirro-cumulus

Derived:
snow.

cumulo-stratus. found in New Zealand and elsewhere, and would naturally ac

(pallio-cirrus sho

Third type stratus. company the diffusion of Malayan dialects throughout Poly

Second type : cumulus (vesicular Derived from nesia, an influence the duration of which may be counted by

the three pallio cumulus aqueous

nimbus. Derived:

tracto-cumulus (vapour.

A. Hall centuries.

types : Dec. II

In forming his system, Prof. Poey first strikes out the Indian Snakes

“stratus” as being from Howard's own definition not a In a small treatise on Indian snakes by Dr. Nicholson, R.A., | true cloud, but only “mist;" the “cumulo-stratus" as not the author states his belief that cobras will not seed in captivity differing really from the cumulus ; and the "nimbus” as unless forced to, starving themselves voluntarily to death. He being not a single cloud, but rather a system of clouds. thinks, also, that jugglers in this country either “feed their He retains the word “stratus” as part-descriptive of the cobras with liquid nourishment, or else let them loose when their “cirro-stratus," but in this case it is exclusively restricted lives are in danger,' recapturing them at a future time.

to those instances where the cirrus arranges itself in a To test the correctness of this, I questioned a snake-charmer

stratified form, and is not applied when the arrangement a few days ago, and he informed me that he fed his cobra every

is an extended sheet or continuous layer of considerable week with frogs. His snake had then been recently sed, so he

thickness totally impervious to the sun's rays. A

To this was told to bring it to the bungalow again in a few days. frog (R. tigrina) was procured, and placed in the small basket

latter condition, the new term “ pallium" is applied. in which the cobra was kept. The latter seized it at once ; but In his classification Poey arranges the clouds in the as I was anxious to see the whole process, which could not be order in which they severally appear, from the cirrus, the done whilst the snake was coiled up in the basket, I requested most elevated, its height being from 30,000 to 50,000 feet, the man to place the frog on the ground. As it struggled away to the fracto-cumulus, the lowest of all ; and groups them (the hind limbs of the poor reptile had been broken) the cobra / into three divisions according as they are composed of followed it eagerly, and again and again seized it. The want of ice-crystals, snowy particles, or vesicular vapour. fangs, and the size of the frog, which in its inflated state ex

But the most fundamental change which he has introceeded considerably the circumserence of its enemy, rendered

duced into the system is the pallium or sheet-cloud, in its these attempts ineffectual; so a smaller frog was caught, and placed

two distinct forms of pallio-cirrus, and pallio cumulus, with the cobra in the basket. This was swallowed in a short

according as it is formed from the cirrus or the cumulus. time, the snake pushing its victim against its coils, and working

The pallium is the greyish, or ash-coloured cloud which down the hind limbs by a lateral motion of the lower jaw, very similar to that of a cow chewing the cud.

overspreads the whole sky, and from which rain falls The large frog was now placed in the basket, and the cover continually for hours or days together. On the approach put on, and in about half an hour had followed its companion. of rain the pallio-cirrus is formed by the rapid increase and The cobra's appetite was now appea:ed, for after seizing a third thickening of the cirrus downwards from the enormous frog it let it go, on its croaking a remonstrance.

# “Nouvelle Classification des Nuages suivie d'Instructions pour servir à A laughable incident occurred whilst the snake was following the

l'Observation des Nuages et des Courants Atmosphériques.' Par André frog over the gravel path. A performing monkey belonging to the | Poey, Havane. (Extrait des Annales hydrographiques, 1872.) Paris, 1873. juggler, in a spirit of mischiel, or perhaps fearing that its master's (17 Plauches).

accessions of moisture that take place, by which this high FERTILISATION OF FLOWERS BY INSECTS ice-cold region of the atmosphere over a great extent and thickness, is brought to the point of saturation and condensation. Underneath this leaden-hued mass of cloud which uniformly covers the sky, but separated More conspicuous flowers adapted to cross-fertilisation, and less from it by a clear space, is extended the dense cloud conspicuous ones adapted to self-fertilisation, occurring in diffecovering of the pallio-cumulus, which is formed by the rent species of the same genus. watery vapour of the atmosphere reduced to the points of condensation and precipitation. This is the true rain

W HAT has been described in the two last articles as cloud, and it is fed and increased by the rapid drifting in

occurring in varieties of the same species (using

| the term “species" in its widest sense) we propose now from below of torn masses of cumulus constituting the fracto-cumulus or wind.cloud. The fracto-cumulus may be

| to investigate as existing likewise in species of the same of all sizes, has no determinate shape, is the lowest and ) genus. swiftest moving of the clouds, and is whitish, greyish, or

Malva sylvestris and rotundifolia slate-coloured, as may be determined by the hygrometric are two closely allied, but, as acknowledged by all condition of the air. On the return of fine weather acces- / botanists, undoubtedly good and distinct species, differing sions of vapour by the fracto-cumulus slacken and then in their flowers in a manner similar to the two varieties cease, the pallio-cumulus diminishes in thickness and gra- ' of Lysimachia vulgaris and the other species previously dually clears away, showing through its intervals the considered. In both these species of Malva an oval mass pallio-cirrus above it, which in its turn is broken up, re- of anthers in the first place occupies the middle of the vealing still higher up the delicate tracery of the cirrus. | flower, enclosing the stigmatic branches as yet undeveThe pallio-cirrus is negatively electrical, whilst the pallio | loped and lying close together (Fig. 23). At a later cumulus is positively electrical, the clear stratum between period the stigmatic branches, growing out of and overbeing neutral ; and between these oppositely electrified topping the mass of anthers, spread and bend outwards strata, discharges frequently take place in thunderstorms. and downwards so as to occupy nearly the same place as

The merits of Prof. Poey's work are very considerable, was before occupied by the anthers (Figs. 24, 25). Insects, whether they be regarded as expository of Howard, or therefore, seeking for the honey which is secreted and as a contribution to this difficult branch of meteorology; contained in five cavities between the lowest parts of the and it is just those meteorologists who have paid particu petals (11, Fig. 23) and covered by a fringe of hairs (for), lar attention to the observation of the clouds who will be carry away on their hairy bodies the large prickly pollenreadiest to recognise its merits. It must, however, be con- grains from younger flowers, leaving many of them on the ceded that, as a descriptive classification of clouds, as well stigmatic papillæ of the branches of the style of older flowers, as explanatory of the phenomena they present, Prof. Poey's which they can scarcely avoid grazing in seeking for the work" leaves the subject in a state still too incomplete honey. Hence, in both species, whenever insects frequently to warrant us in recommending his system for general in- | visit these flowers, cross-fertilisation in the mannerdescribed troduction. It is a step in the right direction, and will is largely effected, whereas self-fertilisation can scarcely materially contribute to place this vitally important de- take place, neither spontaneously nor by means of insects, partment of atmospheric physics on a satisfactory footing. | nearly all the pollen-grains having been removed before

Toward this end, what is now urgently wanted is an | the unfolding of the stigmatic branches. Since, however, extensive collection of the data of cloud-phenomena in all | Malva sylvestris and rotundifolia grow for the most part countries, particularly of those clouds interesting in them- in the same locality, and flower during several months selves or from their known relations to weather changes. at the same time, insects flying about and seeking for We have more than enough of unmistakeably pure typical honey are much more likely to find out and visit the highly forms scattered through the pages of weather-literature, conspicuous flowers of M. sylvestris than the far less conbut such do not greatly assist us, in describing and clas spicuous ones of M. rotundifolia; the former, when fully sifying many of the forms of clouds which occur. Hence opened, presenting bright rose-coloured bells of from 40 what is required is faithfully accurate delineations of these to 50 mm. diameter, the latter, on the contrary, light roseforins in their different aspects, and systematic inquiries coloured bells of only from 20 to 25 mm. set on foot into the relations of the forms of clouds to the Direct observation, indeed, fully confirms this supposimode of their formation, to the states of the aqueous tion, the flowers of M. sylvestris being always found in vapour which compose them, and to the varying elas- sunny weather visited by a variety of insects, whereas ticity, temperature, and electricity of the atmosphere. those of M. rotundifolia, especially when growing inter

In connection with this part of the subject, Prof. Poey mixed with M. sylvestris, are commonly overlooked by investigated in 1862-64, by means of the thermo-electric them all. Thus, during the sixlast summers, I have observed pile, the temperature of different parts of the sky under on the flowers of M. sylvestris and collected more than different conditions, and of the clouds which passed across 50 species of insects, many of them very frequently (2 it. Among other highly interesting results, he has shown | Lepidoptera, 3 Diptera, 5 Coleoptera, 40 Apidæ, some that the cumulus, properly so called, and the cumulo- Ichneumonida); while in the same space of time I found stratus of summer are the clouds of highest temperature ; on the flowers of M. rotundifolia but 5 species (4 Apidæ, then follows the fracto-cumulus, except when it comes i Hemipter), and those only in single or a few cases. after the rain which accompanies a thunderstorm, in It is evident from these facts, that wherever our two which case it is of a whitish colour, very rapid in its mo- species of Malva grow together in the same locality, M. tion, much torn at the edges, and partakes of the low rotundifolia would be rapidly extinguished, unless it were temperature prevailing on such occasions. The cirro enabled to produce seed by self-fertilisation; M. sylvestris, cumulus is colder than the cumulus and the cirrus the on the other hand, is so commonly visited and cross-ferticoldest of all the clouds. These are very suggestive re lised by insects that self-fertilisation, if it were possible, sults. We are convinced that the key to the position in would never be effected, or only exceptionally. Accordmeteorology is a better knowledge of the vapour of the ingly natural selection must have preserved and accumuatmosphere in its various states and changes; and the lated those slight individual variations of M. rotundifolia, science will not make the advances it is destined to make which afford facility for self-fertilisation, whereas in M. till meteorologists generally recognise the necessity of sylvestris the possibility of self-fertilisation being quite equipping their first-class observatories with the requisite useless, might be lost, and, indeed, has been, completely appliances for carrying on those physical researches which or nearly lost. Thus in the flowers of M, sylvestris, when are intimately allied to meteorology.

precluded from the visits of insects by covering them with

a net, the anthers remain filled with pollen-grains, and its body which, whilst it is sucking the honey, are pressed never, or only exceptionally, come spontaneously into con- | against the anthers. Now, the place occupied in one of tact with the stigmatic branches, the free ends of their the two kinds of flowers by the anthers, is occupied in the filaments at a later period bending downwards, and the other kind by the stigmas, the same parts of the body of branches of the styles remaining considerably above them the insect which in the long-styled form were pressed (Fig. 24). Conversely in the flowers of M. rotundifolia, against the anthers, come into contact in the short-styled when the visits of insects are prevented, the anthers, with the stigmas, and conversely. Thus it is inevitable filled with pollen-grains, remain in so high a position, that insects effect chiefly what is called legitimate ferand the stigmatic branches bend so far downwards as to tilisation, i.e. transmission of the pollen of the long-styled come abundantly into contact with the pollen-grains, self flowers to the stigmas of the short-styled, and of the pollen fertilisation being thus inevitable (Fig. 26).

of the short-styled to the stigmas of the long-styled form.

Fertilisation by pollen of the same form, however, and Epilobium angustifolium and parviflorum

even of the same flower, is not impossible, and in the differ most strikingly in a similar manner. The flower short-styled flowers even spontaneous self-fertilisation of E. angustifolium, being of larger size, brighter co- | may happen, by pollen-grains falling down from the anthers lour, grouped in long splendid clusters, and exciting upon the stigmas. attention at a great distance, are so largely visited and The same advantage which P. Fagopyrum has attained cross-fertilised by insects* as never to have need of self-fer- by dimorphism (Darwin) or heterostyly (Hildebrand), has tilisation, which has actually become impossible ; the four been gained in the flowers of P. Bistorta by protanstigmatic branches unfolding so long after the maturity drous dichogamy, i.e. by the anthers so far preceding in of the eight anthers, and so far overtopping them, as their development the stigmas that in the first period of to be completely shut out from the pollen of the same the flower (Fig. 28) only mature anthers, at a later period flower. The flowers of E. parviflorum, on the other (Fig. 29) only mature stigmas are present, the anthers hand, being of smaller size, lighter colour, and single, having then commonly fallen off. It is readily seen that are so inconspicuous that insects but very rarely visit them. such flowers also, when perseveringly visited by insects, Accordingly, its four upper anthers so closely surround are always inevitably intercrossed, no other mode of the the four-lobed stigma, which is mature at the same time, transmission of pollen being possible than from younger as to cover it largely with their pollen, whilst the pollen. flowers to the stigmas of older ones. It is only when the grains of the four lower anthers lying on the way to the visits of insects are completely wanting during the first honey, cannot reach the stigma of the same or of another period and the anthers remain clothed with pollen while flower unless transferred by insects.

the stigmas attain their maturity, that self-fertilisation by

insects or even spontaneous self-fertilisation is possible. Polygonum

The least attractiveness for insects, on the contrary, Among the many species of the genus Polygonum among all native species of Polygonum is possessed by which grow in our country there are two, P. Fagopyrum and P. aviculare, its flowers (Figs. 30 and 31) being of small Bistorta, most distinguished by their attractiveness for size, of greenish and white or reddish colour, standing insects, which is due not only to the size and colour of singly on procumbent plants and offering only a small the single flowers and to their collection into handsome quantity of pollen to insects, but, as far as I have been spikes, but also, and even more perhaps, to their abun | able to see, no honey. No wonder that insects are indance of honey secreted by eight globular nectaries at duced only in very rare cases to visit and fertilise them, * the base of the filaments (11, Figs. 26, 27). With re- and that, in compensation for the loss of cross-fertiliference also to the frequent visits paid them by insects, + sation, these little flowers regularly experience sponthese two species have been adapted to inevitable cross-fér taneous self-fertilisation, the three inner anthers lying so tilisation by their visitors, self-fertilisation having at the close to the stigmas that their pollen-grains inevitably same time become difficult or almost impossible. The come into contact with them (Figs. 30 and 31). manner in which this advantage has been attained being' Of the many other native species of Polygonum, which very different in the two species, it is evident that in this are all intermediate, as to their attractiveness for insects, case the adaptation to cross-fertilisation by the visits of between those now described, I will only remark briefly insects cannot have been inherited from the common upon P. Persicaria, which is of more especial interest parents of the genus, but must have been acquired by the because of its flowers presenting great differences of single species during their evolution.

structure. In this species, instead of eight nectaries there P. Fagopyrum has acquired, as shown in Figs. 26 and are only five developed, and these secrete a much smaller 27, the same kind of dimorphism which has been so fully quantity of honey than those of P. Fagopyrum explained by Darwin in Primula 1 and Linum. $ In and Bistorta. Its spikes of flower, moreover, being less both of the two kinds of flowers (which occur only on conspicuous than in those species, the visits of insects different plants) there are three styles and eight stamens, are somewhat rare, even in sunny weather, although far three of the stamens closely surrounding the styles and more frequent than in P. aviculare.t Fertilisation by opening outwards, the five others inserted more outwards, insects, consequently, is by no means secured. Coralternating with the leaves of the perianth and opening responding to this uncertain agency of insects the sexual inwards. An insect, therefore, visiting a flower for honey | organs of the flower are in a remarkably fluctuating conand pushing its head or proboscis between the inner and dition, undecided, as it were, between adaptation to crossouter stamens into the base of the flower, cannot avoid fertilisation by the visits of insects, and to self-fertilisation. being charged with pollen, especially in those parts of Thus, of the eight stamens, sometimes only the five outer

ones are developed, the three others being reduced to rudi• On the flowers of Epilobium angustifolium I have hitherto observed 26 mentary filaments; and this condition is apparently the species of insects, 14 of them belonging to the family of bees, many of them

most favourable to cross-fertilisation, as any honey-seekvery frequently ; on those of E. parviflorum I found only once Meligethes, and once a butterfly (Pieris rapa L.) repeatedly sucking the honey of its ing insect must touch the anthers in every flower with flowers.

one side of its proboscis, the stigma with the opposite + On the flowers of P, Fagogyrum I have observed 41 species of insects, among them 21 Diptera and 12 Apidæ ; on the flowers of P. Bistorta 18 side, to which it thus cannot fail to transfer pollen-grains species of insects, among them 9 Diptera and 3 Apidæ ; many of the visitors of each species very frequently.

* After having repeatedly in vain watched P. aviculare in very hot sunny 1 On the two forms or dimorphic condition in the species of Primula and noons of the month of August 1871, I succeeded in observing some small their remarkable sexual relations (Proc. of the Linn. Soc. vi. (1862); Bot. Syrphida (Ascia podagrica F., Syritta fipiens L., and Melithreptus menPP: 77-79.

thastri L.) visiting its flowers. On the existence of two forms and their reciprocal sexual relation in + I have observed in the flowers of P. Persicaria altogether in species of several species of the genus Linum, Ibid. 1863, pp. 69-83.

insects, among them 7 Diptera, and these as the most frequent visitors.

from the flowers previously visited. Sometimes, also, species the flowers vary and have always varied the three inner anthers are developed, and, completely in size, colour, the quantity of secreted honey, and confilled with pollen, closely surround and spontaneously sequently in their attractiveness for insects. Whenever self-fertilise the two (in rarer cases three) stigmas, in such a varying species the one variety possesses such a cross-fertilisation being thus almost prevented. But degree of attractiveness for insects as to receive sufficiently most of the flowers show an intermediate condition, having frequent visits from then, those variations which afford only one or two of the three inner anthers developed.

[graphic]
[merged small][graphic]
[graphic]
[ocr errors]

23

24 Fig. 23.–Sexual organs of Malva rotundifolia, in their first period, longi

tudinally bisected, seven times natural size. a, anthers : br, branches of the style (st); pe, petals ; n, nectary ; pr, protecting hairs; se, sepals ;

cv, ovary ; fi, filament-cylinder. Fig. 24.-Side view of the same organs in their second period.

Without referring to many other genera which I have ascertained to contain species quite analogous to those just described, * we may, I think, admit as a summary of the recorded facts, the following propositions :- In many

25 FIG. 25.-Side view of the sexual organs of M. sylvestris, seven times

natural size. facility for cross-fertilisation by insects have always been preserved and accumulated by natural selection, whereas the possibility of self-fertilisation has at the same time frequently been lost. Hence we may infer that cross-fertilisation is more advantageous to a plant than self

[graphic][graphic][merged small]

28 Fig. 26.-Side view of the long-styled flower of Polygonum Fagopyrum, two leaves of the perianth having been removed. n, nectaries; a, anthers;

st, stigmas, Fig. 27.-Side view of the short-styled flower. Fig. 28.-Side view of the flower of Polygonum Bistorta in its first period. Fig. 29.-Side

view in its second period. fertilisation. Whenever, on the contrary, another variety tion, whereas cross-fertilisation by insects has frequently of the same species presents so little attraction for in become very difficult, although perhaps never quite imsects as to remain commonly overlooked by them, only possible. Hence we may infer that self-fertilisation is by

no means absolutely disadvantageous to a plant, but only when the offspring of self-fertilisation has to struggle for existence with the offspring of cross-fertilisation.

There is another curious point about the recorded facts. We have seen that more and less attractive flowers adapted to cross- or to self-fertilisation sometimes occur in slightly differing, sometimes in well-marked varieties, sometimes in doubtful, sometimes in good and distinct species.

If we believe the principle of evolution, and view FIG. 30.-Flower of Polygonum aviculare viewed from above. a, outer

anthers; a', inner anthers; st, stigmas. Fig. 31.-The same flower species as originated from varieties, varieties as originated

viewed laterally, two leaves of the perianth having been removed. from slight individual differences, we may consider the such individual peculiarities as induce self-fertilisation recorded facts as presenting and explaining one of the have been preserved and accumulated by natural selec many ways in which previously varying forms have been * Geranium, Stellaria, Cerastium, Rubus, Veronica, Carduus, Hieracium,

transformed by natural selection into different and diverging and others.

species.

HERMANN MULLER

[ocr errors]
« AnteriorContinuar »