160 HETEROSTYLED TEIMORPHIC PLANTS. CHAP. IV. 



the twelve longest, twelve mid-length, and twelve 

 shortest stamens acts very differently on each of the 

 three stigmas ; so that there are three sets of female 

 and of male organs. Moreover, in most cases the six 

 stamens of each set differ somewhat in their fertilising 

 power from the six corresponding ones in one of the 

 other forms. We may further draw the remarkable 

 conclusion that the greater the inequality in length 

 between the pistil and the set of stamens, the pollen 

 of which is employed for its fertilisation, by so much 

 is the sterility of the union increased. There are no 

 exceptions to this rule. To understand what follows 

 the reader should look to Tables 23, 24, and 25, and 

 to the diagram Fig. 10, p. 139. In the long-styled form 

 the shortest stamens obviously differ in length from 

 the pistil to a greater degree than do the mid-length 

 stamens ; and the capsules produced by the use of 

 pollen from the shortest stamens contain fewer seeds 

 than those produced by the pollen from the mid- 

 length stamens. The same result follows with the 

 long-styled form, from the use of the pollen of the 

 shortest stamens of the mid-styled form and of the 

 mid-length stamens of the short-styled form. The 

 same rule also holds good with the mid-styled and 

 short-styled forms, when illegitimately fertilised with 

 pollen from the stamens more or less unequal in 

 length to their pistils. Certainly the difference in 

 sterility in these several cases is slight ; but, as far as 

 we are enabled to judge, it always increases with the 

 increasing inequality of length between the pistil and 

 the stamens which are used in each case. 



The correspondence in length between the pistil in 

 each form and a set of stamens in the other two forms, 

 is probably the direct result of adaptation, as it is of 

 high service to the species by leading to full and 



