298 



RECIPROCAL BIMORPmSM 



with long stamens; the two having differently sized pollen- 

 grains. With triniorphic plants there are three forma 

 likewise differing in the lengths of their pistils and stamens, 

 in the size and color of the pollen-grains, and in some 

 other respects; and as in each of the three forms there are 

 two sets of stamens, the three forms possess altogether six 

 sets of stamens and three kinds of pistils. These organs 

 are so proportioned in length to each other that half the 

 stamens in two of the forms stand on a level with the 

 stigma of the third form. Now I have shown, and the 

 result has been confirmed by other observers, that in 

 order to obtain full fertility with these plants, it is neces- 

 sary that the stigma of the one form should be fertilized 

 by pollen taken from the stamens of corresponding height 

 in another form. So that with dimorphic species two 

 unions, which may be called legitimate, are fully fertile; 

 and two, which may be called illegitimate, are more or less 

 infertile. With trimorphic species six unions are legiti- 

 mate, or fully fertile, and twelve are illegitimate, or more 

 or less infertile. 



The infertility which may be observed in various dimor- 

 phic and trimorphic plants, when they are illegitimately 

 fertilized, that is by pollen taken from stamens not cor- 

 responding in height with the pistil, differs much in degree, 

 up to absolute and utter sterility; just in the same manner 

 as occurs in crossing distinct species. As the degree of 

 sterility in the latter case depends in an eminent degree on 

 the conditions of life being more or less favorable, so I 

 have found it with illegitimate unions. It is well known 

 that if pollen of a distinct species be placed on the stigma 

 of a flower, and its own pollen be afterward, even after 

 a considerable interval of time, placed on the same stigma, 

 its action is so strongly prepotent that it generally annihi- 

 lates the effect of the foreign pollen; so it is with the pollen 

 of the several forms of the same species, for legitimate 

 pollen is strongly prepotent over illegitimate pollen, when 

 both are placed on the same stigma. I ascertained this 

 by fertilizing several flowers, first illegitimately, and twenty- 

 four hours afterward legitimately, with pollen taken 

 from a peculiarly colored variety, and all the seedlings 

 were similarly colored; this shows that the legitimate pollen, 

 though applied twenty-four hours subsequently, had 



