« AnteriorContinuar »
included as yet published, and will, I trust, therefore, be of value and interest to many, even quite independently of its connection with the preceding papers.
The arrangement of the table will be easily understood. All the figures, with the exception of those in columns 2 and 19, give the number of grammes of the different substances named at the heads of the columns contained in 1000" (1 litre) wine. By shifting the decimal point one figure to the left, we therefore obtain percentages; and by multiplying the figures by 12, the number of grains of the various constituents contained in one bottle of wine are obtained. (Au ordinary wine-bottle holds about 12,000 grains.) Column 2 gives the specific gravity of the wine, i.e. the weight of 1000". In column 19 will be found the proportion per cent, which the alcohol in column 17 bears to that in column 18; in other words, it will show us at a glance how near to, or how far from, equilibrium the process of etberification was at the time of examination (in these cases, the latter half of 1867). Lastly, as regards column 1, I have contented myself with simply giving the generic name of the wine, together, when possible, with the year of vintage, and the retail price per dozen in London- Everyone may thus, to a great extent, judge of the quality of the wine analysed by the price appended. The wines were selected with great care, to ensure, as far as possible, their genuineness; but, for obvious reasons, the sources whence they were derived are withheld.
THE FERTILISATION OF VARIOUS FLOWERS BY
BY WILLLVM OGLE, M.D., F.R.C.P.
AVERY short time ago it was considered a sufficient explanation of the various colours and forms of flowers to say that they were devised to please the eye of man by their brilliancy and their variety. This no longer satisfies us. For we have learnt from Mr. Darwin, that every detail of structure in an organism exists purely and solely for the sake of that organism itself, or because it was of use to the ancestors of the organism, and has been derived from them by inheritance. If anyone bear this general law in mind, and examine by its light a number of different flowers, he will, I think, be led inevitably to two conclusions. Firstly, he will be convinced that the purport of a nectary is to attract insects, and that those flowers which possess one require the visits of insects for their due fertilisation. A second conclusion will be this: That any notable irregularity of the corolla is also—-if not invariably, yet usually—connected with the visits of insects, and has, like the nectary, for its ultimate object fertilisation by their agency. The manner in which the irregularity acts is not always the same. One very common result of it is to compel the insect to visit the nectary in some particular direction by barring up all others, that particular direction being such that the insect is made to impinge in a useful way upon stigma or upon anthers, as the case may be. Another very frequent purport of the irregularity is to compel the insect to alight on a particular part, where its weight causes certain mechanical effects by which the pollen is transferred to the body of the insect and is then carried off to the stigma, perhaps sometimes of the same, but more frequently of some other, blossom.
This view of the purport of irregularity throws light on a fact noticed in manuals of botany, but hitherto, so far as I know, un
.explained, viz. the manifest connection which exists between the presence of nectaries and irregularity of the corolla. "It is to be remarked,"* says A. de Jussieu, "that the development of a nectary on any particular part, stands frequently in intimate relationship with the irregularity of the flower, and seems to determine irregularity on that side where it is situated." This intimate connection of two structural peculiarities becomes perfectly intelligible if it be admitted, as urged above, that the two have one common object, viz. the promotion and utilisation of the visits of insects.
I have already in two former numbers of this Reviewf given sundry illustrations of the preceding remarks. To those illustrations I would now add some others. Combining these with the former, I shall, I think, have shown reasons for concluding that nectaries and irregularity have for their final cause the promotion of intercrossing, and that the same purpose is often subserved by other structural peculiarities which might at first seem matters of indifference. Such, for instance, are the coherence of the anthers (e.g. Gesenria, Composita); their irregularity in form (e.g. Erica, Salvia), in number, length, or general arrangement (Didynamia); their mode of dehiscence (e.g. Vaccinium, Arbutus, &c.), its period (e.g. Digitalis), and the direction of their dehiscent surfaces (e.g. Thyme, &c). Such also are the set of the flowers on the stem (e.g. Melampyrum and Pedicxdaris); their mode of inflorescence (capital); the distribution of their colouring (Pelargonium), and perhaps even the size of the calyx (Pedicularis).
I have already pointed out J how in Thyme and Marjoram intercrossing is much facilitated by the close crowding together of the flowers, in some of which the stigmas, in others the anthers, are alone mature: because a bee, crawling over the flowery surface, must inevitably convey pollen from blossom to blossom. The still closer crowding of the capital and the umbel may perhaps have a similar result. If it be so, we are furnished with the raison d'etre of these modes of inflorescence.
As far, at any rate, as regards the capital, facts, I think, justify this supposition. If we examine a flower-head in any of the thousand composites, we find as follows: Firstly, in each individual hermaphrodite flower the pollen ripens and is exposed before the stigma is mature. Secondly, the different flowers in the same head do not expand simultaneously, but the expansion begins with those of the circumference and extends centripetally. There are thus collected together flowers in every stage. Some in the centre, not yet open: outside these a ring of others, in "Botanique," ninth edition, p. 312.
t See the July number of last year, and the January number of this year. J P. 63.
VOL. X.—NO. XXXV. M