run into one another, or at least that they are divided by such a nice barrier, that it is no sooner touched than passed. Formerly a plant and an animal appeared as beings essentially different, and widely distant from one another; but the tribe of Zoophyta have now extenuated the distinction. Philosophers to this day are fighting strenuously, whether these bodies should be considered as animals or vegetables. The truth, I think, is, that they are neither, but an amazing mixture of animal and vegetable nature; which lays the most natural, and the firmest foundation I know of for an analogy between the two kingdoms. I am now afraid I rather tire than entertain your Lordship; but I own these speculations are so pleasant to myself, that if I did not reflect, I might be led on to a letter which would reach to Edinburgh I mean not by the post, but by actual extension: I would otherwise have added here some further observations on that hiatus in the scale of being which subsists between the most perfect animal and man; and likewise on that illimitable and unfathomable gulf which is interposed between the most perfect creature and the Crea tor. I shall now subjoin, as your Lordship desires, a list of the apparently instinctive motions of plants,, confining myself to such as are most, remarkable, most obvious, and most unquestionable. 1. The leaves of trees and herbs have an upper and under surface; the one constantly turned to the heavens, the other to the earth. If a branch of a tree is bended, and so fixed, that this order of its leaves is inverted, and the under side exposed to the heavens, by a wreathing motion of their footstalks, they will all in a little time recover their former and natural direction. This, I am satisfied from repeated observations and experiments, is owing to an attraction between the upper surface of leaves and light, though it is ascribed by others others to different causes. If a plant in a flower-pot is placed in a window, in a few days the upper surface of all its leaves will be directed to the window. Let it be so turned about, that the under side of the leaves point to the window, in a few days they will all resume their former position. 2. Many plants upon the sun's recess alter the position of their leaves, which maintain a different form during the night from what they observe during the day. This is termed the Somnus Plantarum. Every body since Pliny's time has observed it in a field of clover. 3. Every seed when it germinates, shoots forth a plumula and a radicle: The first, the embryo of the stem, which always ascends; the other, of the root, which always descends. It is amazing how hard these little tender bodies will struggle against the most powerful obstacles which may offer to obstruct or alter these two directions. 4. The seeds of all plants, when sown in the earth, will rise when within a certain depth, but will not rise if placed beyond it. I know, for example, that barley will rise, though sown to the depth of ten inches, but will not rise if placed twelve inches deep. 5. The claspers of briony have both a progressive and retrograde motion. They shoot forwards in a spiral, to lay hold of whatever comes in their way for their support; but if they meet with nothing, after completing a spiral of about three circles, they alter their plan, and shoot away in another direction; that if they miss one way, they may hit the other. 6. Among the ruins of the old monastery of New Abbey, in Galloway, there is a plane-tree, about twenty feet high, which grows on the top of a wall built with stone and lime. Being straitened for nourishment in this situation, many years ago it shot forth roots into the open air. These did neither die nor draw back, but descended by the side of the wall, which is ten feet high. It was se veral years before they reached the ground, during which time they conveyed no nutriment to the tree, but were supported by it. At length they dipped into the earth, and have since enabled the tree to grow with vigour. Between the top of the wall and the surface of the earth, they have never thrown out either branches or leaves, but have coalesced into a sort of trunk ten feet high, and pretty thick; which is very singular, in being now terminated by roots, both at top and bottom. 7. The leaves of many plants, especially of the mallow tribe, move daily with the sun, following him with the upper surface of their leaves, from east, by south, to west. 8. The petals of many flowers expand in the sun, but contract at night, or on the approach of darkness or rain. This is evidently to protect the tender parts of the fructification from injury. 9. But when once the seeds are fecundated, though the petals still subsist, they no longer contract. This is one of the finest instances I know of these instinctive motions, and one of the strongest evidences of the sexes of plants. 10. Every honeysuckle twig shoots straight forward, till it becomes too long to support its weight. It then immediately curls into a spiral: for the spiral figure gives it further strength. If alone, or if it meet with a dead branch, it screws always from the right to the left; but if it meets with another twig, they coalesce for mutual support, and the one screws to the right, and the other to the left. 11. Dodart first observed that trees pushed their branches in a direction parallel to the surface of the earth. If a tree stands on a steep, it pushes both towards the hill, and towards the declivity; but on both sides it still preserves its branches parallel to the surface. As there is an attraction between the upper surface of leaves and light, I am also persuaded, though not equally certain of it from experiment, that there is an attraction of the same nature between the under surface of leaves and the surface of the earth. This I consider as the cause of the phenomenon. I had long observed, that the most fruitful orchards, and the most fertile trees, are those planted on a declivity, and the steeper it is, though not quite a precipice, the more fertile they prove. But I was never satisfied as to the cause of it, till I called to mind the above observation of Dodart; which occurred to me when I was in the town of Jedburgh. There is more fruit about that place, and more fruit-bearing wood upon the trees, than I have seen in any other part of Scotland: But its orchards and fruit-gardens are mostly situated in very steep places. It is well known that the spreading of trees always renders them fruitful. On a plain, however, they incline to shoot upwards; and therefore art is called in by skilful gardeners, and applied in various ways to check their perpendicular, and to promote their lateral growth. But this point, which can only be gained upon a plain by art, is obtained upon a declivity by Nature. There a tree loses its tendency to shoot upwards, and in order to preserve its branches parallel with the surface, is constrained to put them in a lateral di rection. Hence an important rule in the choice of orchards and fruit gardens. I ever am, with the most sincere respect, my Lord, &c. JOHN WALKER. II. II. Lord KAMES to Sir JAMES NASMITH of New Posso, Baronet. On the Analogy between Animals and Vegetables. DEAR SIR, Blair-Drummond, September 27. 1773. THE rich, by Christian duty, are bound to supply the wants of the poor. My wants are urgent; your treasures are great; and I trust I shall find your charity proportionally liberal. It is the quality, too, of that wealth of yours I chiefly covet, that it may be freely imparted without impoverishing the giver. But to come to the point without further preface. I have been thinking a good deal of late, now that I have some leisure for amusement, on a comparison between animals and vegetables, with respect to the curious principle of instinct. You, of all mankind, are the best fitted to give me clear ideas upon the subject; and, therefore, without scruple, I will throw out my crude notions, to prompt you to an opening of your stores my benefit. for be Many are the actions of brute animals, and even of the human race, that are directed by blind instinct, without the intervention of reason or reflection; and I think actions somewhat similar may discovered in vegetables. The growth of plants, their production and decay, come not under my consideration; but certain motions varying from the ordinary course of Nature, like voluntary actions in animals. All roots, when, in their direct progress, they meet with a ditch, and are laid open to the air, immediately dip and hide themselves |