Chap. VI. ON HETEEOSTTLED PLANTS. 245 



lised by any other individual of the same species. This 

 is not so with heterostyled plants ; a long-styled, mid- 

 styled or short-styled plant cannot fully fertiKse or 

 be fertilised by any other individual, but only by 

 one belonging to another form. Thus the essen- 

 tial character of plants belonging to the heterostyled 

 class is that the individuals are divided into two or 

 three bodies, like the males and females of dioecious 

 plants or of the higher animals, which exist in approxi- 

 mately equal numbers and are adapted for reciprocal 

 fertilisation. The existence, therefore, of two or three 

 bodies of individuals, differing from one another in the 

 above more important characteristics, offers by itself 

 good evidence that the species is heterostyled. But 

 absolutely conclusive evidence can be derived only 

 from experiments, and by finding that pollen must be 

 applied from the one form to the other in order to 

 ensure complete fertility. 



In order to show how much more fertile each form 

 is when legitimately fertilised with pollen from the 

 other form (or in the case of trimorphic species, with 

 the proper pollen from one of the two other forms) 

 than when illegitimately fertilised with its own-form 

 pollen, I will append a Table (33) giving a summary 

 of the results in all the cases hitherto ascertained. 

 The fertility of the unions may be judged by two 

 standards, namely, by the proportion of flowers which, 

 when fertilised in the two methods, yield capsules, and 

 by the average number of seeds per capsule. When 

 there is a dash in the left-hand column opposite to 

 the name of the species, the proportion of the flowers 

 which yielded capsules was not recorded. 



The two or three forms of the same heterostyled 

 species do not differ from one another in general habit 

 or foliage, as sometimes, though rarely, happens with 



