PLANTS, organized bodies, of which a full account has been given in the Encyclopædia under the title Botany, Plant, Sexes, &c. The establishment of the sexual system in vegetables, and the acknowledged analogy between vegetable and animal bodies, has suggested a method of improving plants, as animals are confessedly improved, by what is called crossing the breed. This thought occurred first, we believe, to Andrew Knight, Esq.; and in the Transactions of the Royal Society for 1799, we have an account of some very curious experiments made by him, with the view of ascertaining whether the improvement which he had conceived be actually practicable. Those were chiefly made on the garden pea, of which he had a kind growing in his yard; which having been long cultivated in the same soil, had ceased to be productive, and did not appear to recover the whole of its former vigour when removed to a soil of somewhat different quality. On this his first experiment in 1787 was made. Having opened a dozen of its immature blossoms, he destroyed the male parts, taking great care not to injure the female ones; and a few days afterwards, when the blossoms appeared mature, he introduced the farina of a very large and luxuriant grey pea into one half of the blossoms, leaving the other half as they were. The pods of each grew equally well; but he soon perceived that of those into whose blossoms the farina had not been introduced, the seed remained nearly as they were before the blossom expanded, and in that state they withered. Those in the other pods attained maturity, but were not in any sensible degree different from those afforded by other plants of the same variety; owing, he imagines, to the external covering of the seed (as he had found in other plants) being furnished entirely by the female. In the succeeding spring, the difference, however, became extremely obvious; for the plants from them arose with excessive luxuriance, and the colour of their leaves and stems clearly indicated that they had all exchanged their whiteness for the colour of the male parent: the seeds produced in autumn were dark grey. By introducing the farina of another white variety (or in some instances by simple culture), he found this colour was easily discharged, and a numerous variety of new kinds produced; many of which were in size and every other respect much superior to the original white kind, and grew with excessive luxuriance, some of them attaining the height of more than twelve feet.

The difficulty he observed in the offspring, afforded by different kinds of farina in these experiments, pointed out to him an easy method of ascertaining whether superposition (the existence of which has been admitted among animals) could also take place in the vegetable world. For as the offspring of a white pea is always white, unless the farina of a coloured kind be introduced into the blossom, and as the colour of the grey one is always transferred to its offspring, though the female be white, it readily occurred to Mr. Knight, that if the farina of both were mingled or applied at the same moment, the offspring of each could be easily distinguished.

His first experiment was not altogether successful; for the offspring of five pods (the whole which escaped the birds) received their colour from the coloured male. There was, however, a strong resemblance to the other male in the growth and character of more than one of the plants; and the seeds of several in the autumn very closely resembled it in every thing but colour. In this experiment he used the farina of a white pea, which possessed the remarkable property of shrivelling excessively when ripe; and in the second year he obtained white seeds from the grey ones above mentioned, perfectly similar to it. He is therefore strongly disposed to believe that the seeds were here of common parentage; but doth not conceive himself to be in possession of facts sufficient to enable him to speak with decision on this question. We have no right to form a decided opinion on this part of the subject, having paid to it very little attention; but at present we are inclined to think differently from the author. We admit, indeed, that if the female afford the first organized atom, and the male act only as a stimulus, it is by no means impossible that the explosion of two vehicles of farina, at the same moment (taken from different plants), may afford seeds of common parentage; but whether the female or the male affords the first organized atom, is the question which to us appears not yet decided. Another species, however, of superfecundation, in which one seed appears to have been the offspring of two males, has occurred to Mr Knight so often, as to remove, he says, all possibility of doubt as to its existence. In 1797, the year after he had seen the result of the last mentioned experiment, having prepared a great many white blossoms, he introduced the farina of a white and that of a grey nearly at the same moment into each; and as in the last year the character of the coloured male had prevailed, he used its farina more sparingly than that of the white one; and now almost every pod afforded plants of different colours. The majority, however, were white; but the characters of the two kinds were not sufficiently distinct to allow him to judge with precision whether any of the seeds were produced of common parentage or not. In the year 1798 he was more fortunate; having prepared blossoms of the little early frame pea, he introduced its own farina, and immediately afterwards that of a very large and late grey kind, and sowed the seeds thus obtained in the end of summer. Many of them retained the colour and character of the small early pea, not in the slightest degree altered, and blossomed before they were eighteen inches high; whilst others (taken from the same pods), whose colour was changed, grew to the height of more than four feet, and were killed by the frost before any blossoms appeared.

It is evident, that in these instances superfecundation took place; and it is equally evident that the seeds were not all of common parentage. Should subsequent experience evince, that a single plant may be the offspring of two males, the analogy between animal and vegetable nature may induce some curious conjectures relative to the process of generation in the animal world.—It certainly may; but either we do not perfectly understand the author's meaning, or this experiment is not conclusive. There were here seeds of different colours produced by the farinas of different males, operating on the same female plant; and there are well attested instances of twin children being born of different colours, in consequence of the coition of different males, a negro and a white man, with the same woman. Had Mr Knight discovered, not that the same pod, but that the same individual pea, was the offspring of two males, his discovery would indeed have led to some curious conjectures respecting animal generation. But to proceed with his experiments:

By introducing the farina of the largest and most luxuriant kinds into the blossoms of the most diminutive, and by reverting this process, he found that the powers of the male and female, in their effects on the offspring, are exactly equal. The vigour of the growth, the size of the seeds produced, and the season of maturity, were the same, though the one was a very early and the other a late variety. He had in this experiment a striking instance of the stimulative effects of crossing the breeds; for the smallest variety, whose height rarely exceeded two feet, was increased to six feet; whilst the height of the large and luxuriant kind was very little diminished. By this process it is evident, that any number of new varieties may be obtained; and it is highly probable, that many of these will be found better calculated to correct the defects of different soils and situations than any we have at present.

The success of Mr Knight's experiments on the pea induced him to make similar experiments on wheat; but these did not answer his expectations. The varieties indeed which he obtained, escaped the blights of Plague, 1795 and 1796; but their qualities were not otherwise good, nor were they permanent. His experiments on the apple, the improvement of which was the first object of his attention, have, as far as he could judge from the cultivated appearance of trees which had not borne fruit when he wrote his memoir, been fully equal to his hopes. The plants which he obtained from his efforts to unite the good qualities of two kinds of apple, seem to possess the greatest health and luxuriance of growth, as well as the most promising appearance in other respects. In some of these the character of the male appears to prevail; in others that of the female; and in others both appear blended, or neither is distinguishable. These variations, which were often observable in the seeds taken from a single apple, evidently arise from the want of permanence in the character of this fruit, when raised from seed. Many experiments of the same kind were tried on other plants; but it is sufficient to say, that all tended to evince, that improved varieties of every fruit and of elegant plants may be obtained by this process, and that Nature intended that a sexual intercourse should take place between neighbouring plants of the same species.