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that the Dicotyle may themselves be of heterogeneous origin, part of them being descendants of the Conifera, part, of the Gnetaceæ, and part, of the Monocotyle. Should it ever become generally believed that the Dicotyle are of multiple origin, the interest, now so great, in the true arrangement of the families of this class of plants would be greatly increased, and more satisfactory answers to many puzzling questions might be expected.

Perhaps the least objectionable of all the theories advanced, as that which requires the least extreme or improbable assumptions, and affords the greatest relief from the dilemma, is that which maintains the two great co-ordinate branches or parallel ascending series of the vegetable kingdom intact and independent from the most remote period to which they are traceable in the past history of the globe, and sees in the development of the endogenous and exogenous Angiosperms at the summit of each, respectively, the simple attainment in both of one of the great ends of vegetable existence, without which the highest functions of plant life cannot be manifested.

If we believe in the evolution of organic forms at all, we must accept that of vegetable forms, and if we are convinced that the higher plants are the descendants of lower ones, we ought by this time to have at least some provisional hypothesis as to the way in which this process of evolution has been going on in the vegetable world. We should not go on accumulating facts forever without attempting to make any use of them. In this age, when the law of descent has reached, in zoology, its exact stage, the stage of prevision and prediction, it is certainly time that some of the operations of this law were recognized and studied in the cognate kingdom of plants. The utmost that can be objected to any present attempt to trace the genealogy of plants, is, that the precise truth has not been reached, and those who are really competent to raise this objection must be competent to present a nearer approximation to the truth, which is the very service which science most needs. It is, therefore, with a full sense of the imperfection and inherent objectionableness of the scheme, and an entire willingness to see it superseded by one which shall better satisfy all the facts of science, Stripped of all

that the one here rudely sketched is submitted. its complicating conditions and qualifications, many of which have been referred to and explained, this scheme of genealogy

may be more clearly presented by means of the following rough diagram, in which not only are all additional coördinate branches left unrepresented, but the continuation of each stage beyond the point of divergence is, for the sake of perspicuity, removed, leaving the differentiations only to stand in naked outline. This diagram presents the two great lines of descent, that of the Lepidophytes, of which we have the fossil genus Lepidodendron in the Carboniferous, and that of the ferns, trunks of whose arborescent forms are also found in the same formation. The line of the Equisetacea is omitted, although it probably had an independent existence, and may yet be found to have a genectic connection with some of the higher types.

The order of succession here laid down is confirmed by what is known respecting the time at which each of the several groups first appeared in the geological history of the globe. The primary divergence must have taken place in the latter part of the Devonian age, since within this formation occur some remains of Lepidodendron, while fossil trunks both of this and of true tree-ferns are found throughout the Carboniferous strata. It was in this latter epoch that both the ferns and the Dichotomes or Lycopodites attained their greatest perfection and abundance. Whether any of the large trees belonging to either of these groups had advanced to the stage now represented by the Ligulate and Rhizocarpe, there is no means of knowing, but that this stage was reached in both the great lines during the Carboniferous epoch must follow from our hypothesis, since it is within this epoch that both the Conifere and the Cycadacea first made their appearance, and during which they attained to very much the proportions and general character which certain forms of them still present. These forms advanced at a parallel rate and both reached the point of greatest development and supremacy at about the same time in the Triassic and Jurassic periods. They are both at the present time clearly on the decline, especially the Cycadacea, which are on the open road to early extinction before the march of higher types of vegetation. The palæontology of the Gnetacea is little known, but they have been supposed to have originated in the later Permian, or in the Trias. They constitute at best but a transition form, and are not sufficiently abundant to be likely to be discovered in a fossil state. It is a remarkable fact that the earliest remains of both the Monocotyle and the Dicotyle have been found

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DIAGRAM SHOWING THE SUPPOSED LINES OF GENEALOGICAL DESCENT OF VAS

CULAR PLANTS.

in the same formation, viz: the Chalk, and although their first actual appearance may date back into the Jura or Trias, it is probable that in point of time the two great classes of Angiosperms had a nearly simultaneous origin. Whether either of these great vegetable types has reached its highest destiny on the earth it is impossible with certainty to affirm, but the indications are that, for the Dicotyle at least, progress in organization is still going on.

In order to complete the systematic survey of the vegetable kingdom from the point of view of genealogical descent, the following logical scheme of classification is appended for comparison with the genealogical scheme presented on a preceding page:

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THE MODE OF EXTRICATION OF SILKWORM MOTHS FROM THEIR COCOONS.

ITHO

BY A. S. PACKARD, JR.

HOUT having made extended research in the literature of entomology, the only account which we have been able to find of the mode of extrication of the silkworm moths from their cocoons is that given by Kirby and Spence in their chapter on the pupa state of insects, vol. iii, pp. 280-283, which is quoted below, as it gives a summary of what was known up to the year 1828, while so far as we are aware nothing has since then been recorded on this interesting subject, except the observations of Mr. L. Trouvelot (AMERICAN NATURALIST, vol. i, pp. 33, 34); the brief statement in Lacordaire's Introduction a l'Entomology (1834, p. 201) being evidently based on Réaumur's observations.

The texture of the cocoon of the silkworm moth is uniform in every part, and the layers of silk are equally thick at both ends. The moth makes its way out by cutting or breaking these threads at the end opposite to its head; an operation which, as it destroys the continuity of the silk, those who breed these insects are particularly careful to guard against, by exposing the cocoon to heat sufficient to destroy the included pupa. The question is, what instruments does the moth employ to effect this? And this we are not able to answer satisfactorily. Malpighi asserts that the animal first wets the silk with a liquid calculated to dissolve the gum that connects the threads, and then employs its lengthened head to push them aside and make an opening. But, as Reaumur has observed, besides that so obtuse a part as the head of a moth is but ill-fitted to act as a wedge, we find the threads not merely pushed to each side, but actually cut asunder. He therefore infers that the eyes, which are the only hard organs of the head, are the instruments by which the threads are divided-their numerous minute facets serving the purpose of a fine file It should be observed, however, that Mr. Swayne confirms Malpighi's assertion that the silk worm does not cut but merely pushes aside the threads of its cocoon, and he informs us that he has proved the fact by unwinding a pierced cocoon, the thread of which was entire. Yet Réaumur's correctness cannot be suspected, and he affirms that from observation there can scarcely be a doubt that most of the threads are broken; which is further confirmed in an account of the breeding of silkworms published in the American Philosophical Transactions, in which it is expressly stated that cocoons out of which the fly has escaped cannot be wound. Analogy, it must be confessed, is against Réaumur's opinion, since other kinds of silkworms make their

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