PLANT HYBRIDIZATION BEFORE MENDEL 89 



exchanged their whiteness for the color of the male parent; the seeds 

 produced in autumn were dark gray." {ib., p. 197.) 



Here, then, is the first recorded instance of color-dominance in 

 peas. Knight, however, did not follow out the results to the next 

 generation from the selfed hybrids, but re-pollinated the hybrids 

 with pollen from a white variety, as the result of which, he says, 

 there were produced a variety of new kinds, 



"Many of which were, in size and in every respect, much superior to 

 the original white kind, and grew with excessive luxuriance, some of them 

 attaining the height of more than twelve feet. I had frequent occasion 

 to observe, in this plant, a stronger tendency to produce purple blossoms 

 and colored seeds than white ones ; for, when I introduced the farina of 

 a purple blossom into a white one, the whole of the seeds in the succeed- 

 ing year became colored." {ib., p. 197.) 



Here again is an early observation of the fact of dominance, 

 and possibly of heterosis. Knight proceeds to the conclusion that, 

 by mixing the pollen of the two kinds of peas, he could, through 

 the behavior of the seeds, readily determine whether "superfoeta- 

 tion" had taken place or not. In view of the non-existence of 

 "superfoetation," except in the rare cases of dispermy, the experi- 

 ment itself is not of importance, but it brought forth the follow- 

 ing remark, which is interesting as showing Knight's knowledge 

 of the fact of dominance of grey seed-coat color. 



"For as the offspring of a white pea is always white, unless the farina 

 of a colored kind be introduced into the blossom, and as the color of the 

 gray one is always transferred to its offspring, although the female be 

 white, it readily occurred to me, that if the farina of both were mingled 

 or applied at the same moment, the offspring of each could be easily 

 distinguished." {ib., p. 198.) 



Pollinating the flowers of some of the hybrids with the pollen 

 from a white-seeded pea, he says, "The second year I obtained 

 white seeds." Here, he should have obtained gray and white, half 

 and half, but he makes no mention of numbers, since the numeri- 

 cal relations of the seeds did not occur to him as being significant. 



It is interesting to note the results of Knight's experiment in 

 reciprocal crossing. 



"By introducing the farina of the largest and most luxuriant kinds 

 into the blossoms of the most diminutive, and by reversing this process, 

 I found that the powers of the male and female, in their effects upon 

 the offspring, are exactly equal." {ib., p. 200.) 



The vigor of growth, the size of the seeds procured, and the 



