99 taceous insect which Montagu had discovered on the shores of Devon, and described as a species of Oníscus. It is yet, so far as I know, the only member of its genus recognised in systematic works; and, I think, there are among your readers some who will be gratified by having another native one brought under their notice. By The Pranizæ are marine crustacea of minute size. means of their legs, they can creep on the bottom, which they do slowly; but they swim with greater rapidity, propelling themselves forwards by the quick motions of a series of ciliated fins placed beneath the tail. Of their economy, nothing is known. They are characterised by having four unequal antennæ; two sessile eyes; an elongated body divided into three segments, of which the two anterior, or thoracic, are very small, and the third, or abdominal, very large. They have ten legs, a pair to each segment of the thorax, and three pairs to the abdomen; while the jointed tail is armed beneath, and at its end, with foliaceous appendages, that appear to be both motive and respiratory organs. The species may be distinguished thus: 1. P. cæruleàta. — Abdominal segment blue (Lamarck, Hist. Nat., vol. v. p. 168.). Oníscus cæruleàtus (Montagu, in Lin. Trans., vol. xi. p. 15. tab. iv. fig. 2.). — Hab. Shores of Devon. 2. P. fuscata - Abdominal segment reddish brown [Johnston, in Magazine of Natural History, Vol. V. p. 521.]. — Hab. Coast of Berwickshire. The latter is two lines long, subcylindrical. The head, thorax, tail, and legs colourless and transparent; eyes black; the great segment of a reddish brown. Head pointed. Antennæ lateral, four-jointed, the ultimate joint long, and divided by many transverse lines. Eyes lateral, large, compound like those of insects. Thoracic segments very small, with a pair of legs to each: abdomen ovate, with a translucent edge, furnished with three pairs of legs; one from the anterior margin, one from the middle, and one from a projecting tubercle at the base. Legs taper, five-jointed, armed with a simple nearly straight claw. Tail straight, five-jointed; joints equal, distinct, armed on the under side with four rows of compressed fins ciliated on the margins; and the ultimate joint terminated, besides, with four similar appendages, and a triangular process between them. The large segment is, in some specimens, smooth and even; but in others, one of which was selected for our figure, it is raised at the top into two oval bosses that greatly resemble the elytra of a Méloe, and are beautifully punctured. The same parts are visible on the ventral surface in both varieties, but much smaller in that whose back is smooth. It may be a sexual distinction. GEORGE JOHNSTON, M.D. Berwick upon Tweed, April 18. 1832. ART. VII. On the Dispersion and Distribution of Plants. IF we take a general view of the surface and covering of the earth, we shall meet with a perpetual series of flowery valleys, mountains rich in alpine verdure, and forests smiling with the bright and luxuriant tints of the tropics; or sternly resisting, with their dark and sombre foliage, the frozen winds that career over the desolate plains of the north. Wherever we turn, we every where see the same mantle of green spread over the earth; and, even in the most distant lands, our eyes are cheered by that enlivening verdure which adds such a nameless charm to every rural scene. The same wild profusion reigns, and nature teems with never-failing abundance. "Thus spring the living herbs, profusely wild, O'er all the deep-green earth; With such a liberal hand has Nature flung Their seeds abroad." Thomson. But was the scene always so fair? was there always the same display of vegetable riches? or was there a time when the earth was a desolate and barren wilderness, a mass of craggy precipices, rocks piled on rocks, without any trace of organic life? "Where eldest Night, And Chaos, ancestors of Nature, held Of endless waves, and by confusion stood.” This, doubtless, was the state of our globe, for ages before the earth was sufficiently modified to admit of the existence of vegetables. With their original creation we have not at present to do it is our object, in this paper, to discuss the : manner in which vegetables were dispersed over the world; whether by progressive steps from one point, or by one contemporaneous dispersion, spread over the face of the earth. The first of these suppositions will be hardly tenable, if it be fully examined, and the arguments by which it is supported be thoroughly canvassed. The supporters of this theory assert, that, since we are expressly informed that the different animals were dispersed from one original station at the time of the expulsion of our first parents from paradise, that from the same original locality vegetables in like manner emigrated. Now, this appears not only incredible, but perfectly inconsistent with divine beneficence and the Mosaic history. When our first parents were doomed to wander exiles from the happy scenes of their primeval residence, would the Almighty have compelled them to wander over a barren and desolate wilderness? How were they to have obtained the necessary subsistence, if the earth had been a naked rock? They would, beyond a doubt, have perished miserably. There are many theories and hypotheses respecting the land which was then uncovered by the waters of the ocean; some asserting that but a very small portion was left bare. With these visionary dreamings we have no concern: we must be understood to assert that the creation of vegetables was antecedent to that of animals; and that, wherever the land was not covered by the sea, there was to be found abundance of earth's vegetable treasures. Even supposing that the grand dispersion was coeval with the expulsion of our first progenitor, this theory will gain no advantage. The earth, we are well aware, must needs have suffered many important changes before it could support vegetable life; and daily experience proves this change to have been gradual. It is much more reasonable to suppose, that, long previous to the creation of mankind, or even of the lower animals, the earth had, by the store of food universally extended, become adapted to their support. But how does the Mosaic history bear with reference to this? "And God said, Let the earth bring forth grass, the herb yielding seed, and the fruit tree yielding fruit after his kind, whose seed is in itself, upon the earth: and it was so." "And the evening and the morning were the third day." (Genesis, chap. i. ver. 11. and 13.) Here we are told that the earth became covered with grass and herbs of various kinds, without any specification of time or place. Now, the word day, in this passage, appears to signify a certain period or length of time; that is to say, the third period from the creation of the earth: viz., first, the vicissitudes of day and night, since, without light, nothing possessed of life can come to perfection; secondly, the land was separated from the water; then, when it had acquired sufficient consistency, vegetables were scattered over it, which afforded food for animals, the creation of which followed; and lastly came man, to take possession of the whole. Now, what argument do we derive from this? That the earth went through progressive stages, the duration of which we have no means of determining; and was adapted to the existence of man before he himself appeared. Hitherto we have considered the subject in a scriptural and rational point of view : let us now apply botanical reasoning. Supposing it possible that vegetables could have been dispersed originally from one station, and thence become naturalised over the whole world, how would this theory agree with the present state of our knowledge? Were we at this time to find that plants flourished equally well in all countries, unaffected by the changes of heat and cold, climate, and geological structure of the earth; or that the same plants were universally distributed, peculiar to no part of the world, but equally common in all; then we might reasonably and naturally infer that they are citizens of no country, but of the world in general. But how stands the fact? If we cast our eyes over a botanical chart, we shall find that, far from this being the case, many families of plants are peculiar to certain parts of the world, and never extend naturally beyond these boundaries; that some are exclusively confined to one small tract, while others are scattered equally over the face of the earth. Thus, for instance, the Anonacea, Dilleniacea, and the palms are almost entirely confined to tropical countries. The Ericæ are scarcely to be met with out of the Cape of Good Hope: not a single species is found in America or in Asia; and few, comparatively speaking, are natives of Europe. Lastly, New Holland presents a rich and inexhaustible field of discovery. The botany of Australia is so dissimilar to that of every other known country, that it deserves particular attention. Of the plants already known in that country, 400 species are cryptogamic, 860 monocotyledonous, and 2900 dicotyledonous. Of the 400 cryptogamic, more than 120 are also indigenous to Europe; of the 860 monocotyledonous, only 30 have been found in Europe, and more than half of these are grasses and Cyperaceae; but of the 2900 dicotyledonous species, only 15 are the same in Australia as in Europe. (Library of Useful Knowledge, Physical Geography, part ii.) They exhibit but a very meagre acquaintance with the laws which influence the situation and locality of plants, who conceive it possible (though it is a well known fact that plants are very far from indifferent to the changes of heat and cold, and the composition and nature of the soil on which they are found) that they could be assembled originally in one station; or that one single part of the world could afford varieties of climate, soil, and situation sufficient for the support of plants which now are found in the most opposite regions of the earth. It is physically impossible that the same vegetable productions should be found on the sandy downs of New Holland, or in the forests of North America, and on the granitic peaks of the Himalayah chain. However strange this theory may appear, nevertheless it is but just to mention that it was the opinion of the founder of scientific botany. Linnæus very ingeniously, though, in my opinion, unconvincingly, endeavours to prove that plants were originally dispersed from one locality. In maintenance of this theory, he supposes the primary seat of plants to have been in a warm climate (Armenia or Thibet), comprehending a lofty mountain range, on which the plants of different regions were congregated, and from thence spread over the world. (Oratio de Telluris habitabilis Incremento.) If such were the case, we might expect, in the regions in the heart of Asia, to find traces of the vegetable productions of America, New Holland, or Southern Africa; since from the mountain ridge, and the circumjacent plains of Asia, according to this supposition, they originally migrated. It is much more rational to suppose that the creation of them was universal, modified and regulated to suit the character of the soil, composition of the rocks, and temperature of the climate, in which they were intended to multiply. To assist their dispersion, he calls in the aid of winds, rivers, birds, &c.; and makes mention of many curious contrivances in the vegetable structure to enable them to project their seeds to a distance: and supposes, since the seeds of cryptogamous plants are so minute, that they would be conveyed by the agency of the winds to an incalculable distance. To this theory some strong objections may be offered: - 1st, That vegetables could not be dispersed, without a soil calculated to receive and nourish the seeds; 2d, Though the winds are undoubtedly able to convey the seeds of many plants to a great distance, especially those of the class Syngenèsia and natural order Compósitæ, yet of many others they cannot effect the dispersion for even a single mile. I have myself seen, in this county (Yorkshire), a bank covered with the Aquilegia vulgàris, which, though exposed to the most violent action of the winds, never spread over the neighbouring fields. This opinion we cannot, therefore, reasonably admit as the true one: the progressive steps by which vegetation advances are extremely slow; and it |