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greens and other plants, as the cabbage and meadow. account for plants in whose foliage the same congrass, which maintain their verdure at s'ich times ? ditions are wanting, as in evergreens, cabbage, and However, since there cannot in anything well be some of the grasses ? To explain this, I regard it effect without cause, let us seek what ground they as of primary importance that the same facts be afford us of offering an explanation of such a differ- still borne in mind with which I started, coupling ence. In doing this we shall not have occasion to them with considerations such as these :-(1) The look very far before we shall find, in the examination relative difference between the temperature of of the leaves of the first, and I might add, main
the earth and that of the atmosphere; (2) the close class of plants, i.e. the evergreens, 'something connection existing, as a rule, in all such instances tangible to theorize upon. For regarding the leaves (for be it here remembered these plants are mostly of plants — as is generally conceded – as the acauliferous) between underground stem and leaves lungs, through which the functions of respiration
of these plants. For such cases, where we have and exhalation take place, we shall not be long,
the sap laid up in a part so protected as an underI think, before arriving at something like a definite ground stem, from which the leaves do so immeconclusion on the matter.
diately spring, can scarcely fail but to maintain a In the leaves of evergreens, or as I will now call sufficiently vigorous vitality in the leaves them
selves. them for sake of convenience, cold-adapted and heatadapted plants, there has been made a provision account for the reason of petiolate or stalked leaves
Upon an almost similar principle is it that I against too rapid exhalation and inspiration, through falling more readily than those that are sessile—the which they become naturally adapted for both con
two cases being almost parallel. Of course, viewing, ditions-either of heat or cold. Hence, bearing in mind what has just been stated in reference to
as must be done for the sake of analogy, that the the relation which the chlorophyl sustains to ligot, its petiole, as each severally corresponding to the
woody stem to which such a leaf is attached, and warmth, and sap, and also of how this latter stands
protecting nature of the earth on the one hand, and affected to cold, there will be perceived the
the exposed stalk to the subterranean and consefeasibility of the conclusions I am here seeking to
quently protected stem of the other, it will be perestablish ; and to show that, as in cold-adapted
ceived how it stands to sense why such a leaf should plants so in tropical, the same conditions are neces
sooner defoliate than the other, where no such sary to meet either extreme, I need only mention the fact that were it not so, they would not be inter-appendage as a leaf-stalk divides the two, fitted to protect the sap against the too detrimental hardier than the leaf itself
, since both, in point of
because the petiole cannot be regarded as a whit effects of extreme cold on the one hand, or of heat on the other, because the sap in plants, as in arimals
, system, are similarly constituted. is the life; and consequently connected with the
I do not intend that what I have just said should presence or absence of which, in part or whole, will
apply to others than perennials, that is, plants that be the corresponding issues-lise or death, of that
live for many years, and not of those which by part or whole.
nature are limited to a fixed term of one or two The nature of the protection of the leaves of these
years. But even connected with the fruiting and plants, as contrasted with those which are so readily
defoliation of these, and indeed all of them, there is and lengthily kept denuded, will be perceived to
something to be learnt. For is it not notable that consist in their clothing membrane or epidermis defoliation in no case precedes fruiting, but succeeds being formed, in point of texture, much thicker and it? And why? I think the answer is not far to seek, stouter. It of course is this increased thickness eve
even to one very moderately qualified in the rudi. and bardened texture of their epidermis which give
ments of botanical science. Is not the period of the leathery or woody leaves of evergreens their fruiting one in which the secretions are more atpeculiar appearance and consistence, enabling tracted, and perhaps altogether in the case of them to withstand external influences of heat and annuals and biennials, to the fruit ?-hence most cold so long. So in respect of young shoots; these, probably their death. Whereas in the case of when they emerge from the bud, are covered by a others this process of developing and maturing their delicate epidermis, by which they are enabled to fruits would appear to be only so far exhaustive of retain their green colour and succulent condition for the energies of the plant as to partly deprive the some time. Seeing then that the epidermis is so leaves their vitality; and thus aiding their de. specially designed to prevent a too rapia evapora. foliation,-a theory, by the way, which seems to be tion of fluid matters from the tissues beneath, so well substantiated in the case of the holly, which is must it follow that, according to the nature of the known not to shed its leaves till early in the spring, .epidermis will its adaptability or non-adaptability directly after the berries have ripened. Now there be in protecting the sap; just in proportion to is, I know, a very common, though notwithstandwhich being protected, will the greenness and vitality, ing, erroneous impression among some people that or otherwise, of the leaves be made manifest. the holly never sheds it leaves at all; but this
It might be asked, what can be advanced to no doubt arises from the fact of its never being
seen perfectly denuded thereof; for no sooner do partly explanatory of such phenomena, when we the old ones drop than fresh ones appear;-hence don't find, as a rule, such appearance occurring in such a sense it is evergreen.
amongst plants which are herbaceous, or, in other What makes me attach still more importance to words, those in which the parenchymatous system the effects which flowering and fruiting have in predominates throughout; as in these we find all partly aiding defoliation, is due to the case of a equally perishing throughout, without any such sepatree, possessed by a friend of mine, coming under ration of parts. Apparently confirmatory of this my notice only a short time ago. This tree, which we will take the effects of a keen prolonged frost be has had now for close upon four years, has never upon newly-formed wood or young branches; the parted with a leaf during the whole of the time, result being that of its becoming nipped, giving rise yet looks as healthy and vigorous as ever it did. to what bere might also be equally and feasibly Now I cannot account for this on any other ground claimed as the “ Phenomenon of Delignization.” than that of its never having flowered in the time. As to what appropriate warmth, soil, and moisture Certainly the plant is not elbow-jointed where the will do in keeping up the vitality and foliage of leaves join the stem; still I cannot see how this can plants generally, we-have well exemplified at home well be accepted as a main cause. Then there is the in our nurseries, where a case of complete plantquestion of articulation to be considered as effecting nudity would rarely or ever be witnessed. We have defoliation. This ought not, as some seem to do, to but to study the geographical distribution of plants be regarded as fully causative. It may, and indeed in order to gain a correct knowledge of how far no doubt does, after the sap becomes less active soil and climate go towards influencing vegetable through the chilling influence of cold, or other · growth. If, for instance, we were to go to Egypt, causes, induce the leaves to fall more rapidly; still we should there find plants going through the even this would be very much dependent on the phases of their existence in one half the time nature of the wood of the plant. To mention a case they do here. But, on the other hand, we as illustrative of this point, I would allude to the should find, as we proceeded from warmer regions beech-a tree, among others, that retains its leaves towards the poles, that, as the light and heat in a decayed condition throughout the winter, even diminished, the vegetation is checked in the same to the shooting of the buds. Now I am so bold as proportion; proving that it is only where the sun to think that even their points of attachment would
rises highest in the ever-cloudless heavens that vegebecome very much strengthened could but the tation flourishes in the greatest luxuriance, and vitality of the leaves be maintained beyond a year assumes its most majestic form. or so under favourable climatical influences.
I hope that this imperfect paper may be the Then as to trees, there is another thing which means towards eliminating something further on ought not to be lost sight of in the consideration of this most interesting subject through the pages of this subject. I refer to their height, and the in SCIENCE-GOSSIP. creased coldness to which the leaves are as a conse Sheffield.
JOHN HARRISON. quence subjected, all which must have, and espe. cially in cases where the leaves are tender and gifted with “ free lungs," a very great influence in
EXOTIC ENTOMOLOGY.* hastening and prolonging their nudity. In proof
THERE are few living authors who have intrc.
duced more students to the various branches itself from the impoverishing effects of fruiting of natural science than the Rev. J. G. Wood. As before the activity of the sap will be again mani.
an author he has the happy knack of immediately festing itself through the appearance of buds, striking a friendship with his readers, unless, indeed, showing how cold keeps in abeyance the sap, and
they are more captious than usual. The entire chiefly through that causes defoliation and length.
field of zoology has been roamed over by him, and ened nudity, and also where in some instances it
there is hardly one of its corners he has not explored. has reached the plant in its most sheltered parts The wonder is, not that amidst so many books the roots-it has killed it altogether.
written by one man, there should be some errors in Perennials, or those in which such phenomena as
fact and errors in judgment, but that there are so defoliation, &c., take place, are for the most part few. If there is a tendency sometimes to dismiss ligneous or subligneous in their structure; and de
those leading speculations which are agitating the pending upon this is their power of endurance and
minds of the best and most philosophical naturalists resistance. Hence I take it that the leaves, flowers,
in the world, somewhat contemptuously, it is because and fruits, together with their petioles and peduncles, being chiefly made up of a softer tissue,
* “ Insects Abroad; being a Popalar Accoant of Foreign are sooner perishable, and as a consequence fall
Insects." By the Rev. J. G. Wood, M.A., F.L.S. London: away. Especially so does this appear in a measure Longman, Green, & Co.
scarcely wil vegetation have had time to replenish T
Mr. Wood does not pretend much to philosophy; | outcry for "facts” among those who regard erolu. nor do we think he has yet appreciated the many tion as only another name for atheism, as the suzga tive hints which the new school of thought is Roman maiden demanded the brazen shields of silently working out. He is a simple narrator of the soldiers. These people know not what to do
acts, as correctly as he can make them out. These with facts when they are put into possession of are undoubtedly important if well arranged and them, and are borne down to the earth, and help. thoroughly understood. There is a pretended | lessly crushed beneath the overwhelming mass of
"facts” wbich every day are crowding before our may be best judged of by the few blocks which notice.
have been kindly lent us for that purpose by the Mr. Wood is not one of these ignorant pseudo- publishers. The larger illustration shows a group critics : his books always strike one as thoroughly of homopterous insects, chiefly Cicadas; whilst the genuine. Their tone is quietly earnest, and the figures of the Eurytrachelus Titan, a beetle more literary style of them all is most admirable. In his than four inches in length; and the still larger "Insects at Home,” Mr. Wood compiled a large and “Elephant Beetle," Negalosoma elephus-a splendid most useful volume of entomological reference, well insect, black, covered with chestnut and yellow fur written, and equally well and copiously illustrated. —will give the reader fair examples of the average But the shelves of most natural history students merits of the wood-cuts. In fig. 36 we have a specicontain works on British entomology, whereas men of the curious order of Ambulatoria, or walking. exotic entomology has been, in England, but feebly insects, about which so much interest hangs, from represented. Our museums often contain magnifi. the strongly marked mimetic features they display.
The illustration is that of the Eurycantha horrida—a name well deserved, for the insect is thrice the length of its portrait as here given. It is a native of New Guinea, and its eggs are said to be as large as those of the small humming-birds. A peculiar fact marks the larval stage of this insect. If one of the limbs bappen to be lost, it is immediately replaced by another.
In fig. 37 we have the magnificent and well-known black and green butterfly, Papilio palinurus, whose under surface presents such a marked contrast to its upper. Fig. 38 gives us an instance of strongly-marked mimicry, not unlike that which exists in our own male "Orange-tip," or still
more, in some of the tropiई.
cal “Leaf-insects." This Fig. 36. Walking-stick Insect(Eurycantha horrida).
object is Kallima paralekta. The illustration wants some
little explanation, for the cent specimens of tropical lepidoptera; but how artist has represented the butterfly with closed wings, rarely do we find even a few of them properly at rest on a twig, one of whose leaves is mimicked named. Then as regards many other kinds of by the reposing insect. This butterfly, has been insects, the foreign beetles, fireflies, mantids, ants, already described in Wallace's "Malayan Archipe&c., the only information we have is sparsely scat. lago.” It occurs in dry woods and thickets, and so tered through books of travel, or meagrely given in wonderfully do its markings protect it; that even brief sketches.
Mr. Wallace, trained and skilled: entomologist We hail Mr. Wood's book on foreign insects, though he is, could not find this insect when he was therefore, with much pleasure, believing that a pursuing it, and it happened to alight even near bim ! popular well-written work of this kind was much The general reader will peruse this volume with wanted by the intelligent reader; and that Mr: much interest and pleasure; and the young naturalWood was just the man to write it. It is a com ist will often turn to ii for information that he can panion volume to "Insects at Home," containing with difficulty procure elsewhere. Of course the nearly 800 pages, with six hundred illustrations and author does not pretend to do other than delineate full-sized plates. The letter-press is clear and plea- the best representatives of each order. To do more, sant to the eyes, whilst the style of wood-cutting especially in exotic entomology, would prove a task