HYBRIDISM 35 



Reciprocal Dimorphism and Trimorphism 



This subject may be here briefly discussed, and will 

 be found to throw some light on hybridism. Several 

 plants belonging to distinct orders present two forms, 

 v/hich exist in about equal numbers and which differ in 

 no respect except in their reproductive organs; one form 

 having a long pistil with short stamens, the other a short 

 pistil with long stamens; the two having differently sized 

 pollen grains. With trimorphic plants there are three 

 forms 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 necessary that the stigma of the one 

 form should be fertilized by pollen taken from the 

 stamens of corresponding height ia 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 legitimate, or fully 

 fertile — and twelve are illegitimate, or more or less in- 

 fertile. 



The infertility which may be observed in various 

 [dimorphic and trimorphic plants, when they are illegiti- 

 mately fertilized, that is, by pollen taken from stamens 



