88 PLANT HYBRIDIZATION BEFORE MENDEL 



Twenty-five years earlier, in 1799, Knight undertook experi- 

 ments with plants to test the theory of "superfoetation," that is 

 to say, the possibility of two males combining in the fecundation 

 of a female. At the time, the behavior of the fertilizing cells was 

 absolutely unknown, as was the fact that but one sperm cell was 

 required to fertilize the egg. In fact, cells as such, and their func- 

 tion, were not as yet discovered. It was quite commonly supposed, 

 for instance, that an excess of pollen in pollination produced an 

 excess effect amounting to a preponderating evidence of the male 

 characters in the offspring. 



Peas were chosen for the purpose of the experiment in ques- 

 tion. The principal object was to obtain new and improved vari- 

 eties of apples, but inasmuch as years must elapse before the 

 results would become known, it was resolved, in the interval, to 

 experiment with annual plants. 



"Among these," he says, "none appeared so well adapted to answer 

 my purpose as the common pea ; not only because I could obtain many 

 varieties of this plant, of different forms, sizes and colors ; but also be- 

 cause the structure of its blossoms, by preventing the ingress of insects 

 and adventitious fauna, has rendered its varieties remarkably perma- 

 nent." (3a, p. 196.) 



Having a variety in his garden which appeared to him, from 

 having been long grown in the same soil, to have lost its vigor, 

 he emasculated a dozen flowers upon it in 1787, pollinating half 

 of them with the pollen from "a large and luxuriant grey pea," 

 leaving the other half dozen as they were. The ovules in the 

 pods of the unfertilized flowers, withered, of course. 



"Those in the other pods attained maturity, but were not in any sen- 

 sible degree different from those afforded by other plants of the same 

 variety, owing, I imagine, to the external covering of the seed (as I have 

 found in other plants) being furnished entirely by the female." {ib., 

 p. 197.) 



Knight was thus induced to take up garden peas for his ex- 

 periments, for the same reason, as stated, that led Mendel later 

 to do likewise. His reflections upon the reason for the act of fer- 

 tilization by pollen from the grey-seeded pea (i.e., with grey seed- 

 coats) not affecting the fertilized ovules in respect to their seed- 

 coats, show the mind of an acute observer. 



"in the succeeding spring the difference, however, became extremely 

 obvious ; for the plants from them rose with excessive luxuriance, and 

 the color of their leaves and stems clearly indicated that they had all 



