504 PHILOSOPHICAL TRANSACTIONS. [ANNO 17QQ. 



bright red heat, I think we may very safely conclude, that all attempts to discover 

 any effect of heat on the apparent weights of bodies, will be fruitless. 



XII. Experiments on the Fecundation of Vegetables. By Thomas Andrew 



Knight, Esq. p. 195. 



In this paper Mr. K. gives an account of some experiments on plants, which 

 prove the existence of super-foetation in the vegetable world, and which seem likely 

 to conduce to improvements in agriculture. 



The breeders of animals, (says Mr. K.,) have very long entertained an opinion 

 that considerable advantages are obtained by breeding from males and females not 

 related to each other. Though this opinion has lately been controverted, the 

 number of its opposers has gradually diminished; and I can speak from my own 

 observation and experience, that animals degenerate, in size at least, on the same 

 pasture, and in other respects under the same management, when this process of 

 crossing the breed is neglected. The close analogy between the animal and vege- 

 table world, and the sexual system equally pervading both, induced me to suppose, 

 that similar means might be productive of similar effects in each; and the event has, 

 I think, fully justified this opinion. The principal object I had in view, was to 

 obtain new and improved varieties of the apple, to supply the place of those which 

 have become diseased and unproductive, by having been cultivated beyond the 

 period which nature appears to have assigned to their existence. But, as I foresaw 

 that several years must elapse, before the success or failure of this process could 

 possibly be ascertained, I wished, in the interval, to see what would be its effects on 

 annual plants. Among these, none appeared so well calculated to answer my pur- 

 pose as the common pea; not only because I could obtain many varieties of this 

 plant, of different forms, sizes, and colours; but also, because the structure of its 

 blossom, by preventing the ingress of insects and adventitious farina, has rendered 

 its varieties remarkably permanent. I had a kind growing in my garden, 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 a 

 somewhat different quality; on this, my first experiment, in 1787, was made. 

 Having opened a dozen of its immature blossoms, I destroyed the male parts, 

 taking great care not to injure the female ones; and, a few days afterwards, when 

 the blossoms appeared mature, I 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 I soon perceived, that in those into whose 

 blossoms the farina had not been introduced, the seeds remained nearly as they 

 were before the blossoms 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, I imagine, to the ex- 

 ternal covering of the seed, as I have found in other plants, being furnished en- 



