away he travels to fix his residence in remote parts. A plant of this kind, the Erigeron Canadense, Linn. was received from Canada, about 100 years ago, into the Paris garden. It is now spread as a wild plant over France and Holland, over Germany and Italy; it is said over Sicily; and to such a degree over the south of England, that it is now enumerated in the English lists of indigenous plants. Some seeds, such as the clot-bur, are of an adhesive nature; they lay hold of animals that come near them, and they are carried off, and spread far and wide.

Many other agents are employed by nature to preserve the earth completely stocked with plants. The sea and the rivers waft more seeds than they do sails from one part of the world to another. I have found seeds dropt accidentally into the sea among the West India Islands, cast ashore on the Hebrides.-The Island of Ascension is but the dross of a volcano, and that of a recent date. Its immense distance from land, must render its acquisition of vegetable seeds very difficult and precarious. I know but two ways in which it could be supplied with plants by Nature. The one by the waters of the ocean, the other by birds. By one or other of these ways, it has now got possession of three species of plants, and only three: A singularity no where else known on the face of the globe.

The animal creation is supported by the vegetable: but in return, the vegetables owe much of their progress and propagation to animals. Nay, while an animal is supported by the apparent destruction of a vegetable, he is, in fact, only the instrument of its further propagation. The swine, the moles, the mice, the squirrels, and a thousand other animals, are constantly at work, though with other views, upon this employment. But among all the animals, the birds and graminivorous quadrupeds are the prime agents in the dissemination of plants.

Many birds live upon fruits and berries. The pulp is their aliment: But they discharge the seeds unimpaired, and by that means spread them every where abroad. These seeds are heavy, and not provided, like others, with any apparatus for flight. But all this is abundantly supplied by the birds which devour them. Hence the bacciferous trees and shrubs appear sometimes whimsical in the choice of their situation. I have seen plantations of holly, yew, whitebeam, rowan, or mountain-ash, spindle-tree, hawthorn, and juniper, formed by the birds of the air, upon inaccessible precipices and impending cliffs, which far excelled, and even disgraced, in point of beauty, the plantations of men.

The mistletoe of old was deemed also, by the wise men, a product of equivocal generation; because it grew upon trees, and had no flower which they could perceive. They saw, indeed, its large, round, heavy berries. These they thought might fall to the ground, but never could mount up into trees; and it was therefore concluded, that they were not the seeds of the plant. It was long since discovered, however, that no berries are more grateful to the birds of the thrush kind; and it is by them they are evacuated, and planted upon high and remote trees...

It is remarkable, that the vegetating power of seeds, instead of being impaired by their passing through birds, seems rather increased. The seeds of the magnolias brought from America, have generally refused to vegetate under the management of the most skilful gardeners. But I have been told a curious fact, brought from America by Lord Adam Gordon, That when these seeds are eaten and voided by turkies, they never fail to grow. As your Lordship is intimate with Lord Adam, you may be more certainly informed of this remarkable observation.

It is well known, that the dung of domestic animals, while it fertilizes a garden, likewise fills it with a great quantity and variety of weeds. All the seeds they eat, which are various and numberless, are discharged entire, and not less fit for vegetation. This to me is a miracle in nature; that seeds should withstand the power of animal digestion, which no other vegetable substance can, and which they are also unable to do once they are broken. This is such a provision for the preservation and dissemination of seeds, as I cannot look upon without wonder.

Thus much for the propagation of plants; any other method except by seeds, suckers, and layers, appears to me both unknown and unnecessary. And so farewel to equivocal generation. I can scarce write of it without being a little ruffled. So ill it corresponds with

the more august and comfortable ideas of creation, which have made one of the principal articles of happiness in my life. I am afraid of going into detail upon the second article of your paper. My mind upon the subject is shortly this.

The ultimate particles of the solids of all animals and vegetables, as far as glasses can go, appear organized :-That they were once unorganized is unquestionable; for I allow of no organization, but what is perceptible to the eye, or by its effects:-That they are organized by the plant or animal, and lose their organization upon its dissolution:-That they have no power to organize themselves :-That they are purely passive, and formed into an organic body, by the assimi-lating power of the plant which assumes them :-All these points. correspond with your Lordship's opinion in your letter. They may be misunderstood and controverted; they may be obscured by ingenuity, and opposed by one hypothesis piled upon another; but if I know any thing of Nature, they are positions which will stand the

test..

As.

As to the infinite series of embryo's in the seed of a plant, I have the same opinion of it as your Lordship. It is invisible and incomprehensible, two unlucky properties in a material subject; nor can it have any effects assigned to it which we cannot deduce from a more palpable and rational cause. I always looked upon it as a silly conceit, which arose from viewing the plantula in semine. I am so far from thinking that future plants subsist in a seed, that I am persuaded that the plant immediately produced from a seed does not subsist in it, in its perfect form, and in all its parts. The plume and radicle do indeed subsist in it, and these have a power to produce all the parts of the plant complete. We can by culture, by cutting, clipping, and different ways, give such various forms to a plant, that to imagine these, or any one of these subsisted in miniature in the parent seed, is perfectly visionary.

Your Lordship next puts a puzzling question-By what cause does a seed begin to vegetate in the earth? Here the primum mobile is to me perfectly mysterious. I cannot form even in idea any explanation of it that is satisfactory. The original cause I doubt is placed beyond our view, but the secondary or immediate cause lies within our reach, and may be ascertained.

1

Animals have a circulation; but plants, so far as I have yet found, only a progressive motion of their juices. Harvey placed the life of animals in the circulation of the blood: and the opinion has ever since generally been received in medicine. Our great medical friend*, however, now demonstrates that it is an opinion void of foundation. The nerves in animals are a system of vessels upon which life does more immediately depend, than either the blood'vessels or their contents. But as there is no such system in plants, I hold with respect to them the doctrine of Harvey; and am of opinion

* I presume, Dr CULLEN,

opinion that life in them consists immediately and essentially in the motion of the sap. What is then the immediate cause of vegetation, that is, of the motion of the sap? I answer, heat.—Heat, figuratively speaking, is the heart of vegetables. It is the cause that moves and propels their sap into a progressive motion, as the heat does the blood of animals, into a motion that is circulatory. Thus far we can go, and I believe no farther.. In both cases, the remote cause of motion is secret, and far removed from all human inspection.

The ascent of the plume and the descent of the radicle, is indeed a surprising phenomenon; yet I think it may be accounted for upon a mechanical principle. To ascend and descend is not the ultimate view of these two parts in their growth; but the endeavour of the one is to get into the air, and of the other into the earth. And to attain these two ends, as seeds are generally deposited in or near the surface of the ground, the plume must ascend, and the radicle descend. But place seeds in the roof of a cave, or in an inverted flower-pot. What is the consequence?. I know it well from repeated observation. The radicle ascends, and the plume descends : That is, the first pursues its road into the earth, and the other into the air, in whatever direction the air and the earth are placed. There is therefore a sympathy, an attraction, or if these displease, something, I know not what, between the plume of a plant and air. But by whatever name it may be called, it is the immediate cause of plants shooting into that element, and quite different from a mere tendency to shoot upwards.

The point at the juncture of the two cotyledons, or seminal leaves, is the place from whence the plume and radicle spring; and this I look upon as the punctum saliens vitæ, both in seeds and plants. Here the radicle ends and the plume begins. I have examined, but

have