24 HETEEOSTYLED DIMORPHIC PLANTS. CHAP. I. 



likewise be apt to cause the self-fertilisation of both 

 forms. 



The several foregoing facts led me to try the effects 

 of the two kinds of pollen on the stigmas of the 

 two forms. Four essentially different unions are pos- 

 sible; namely, the fertilisation of the stigma of the 

 long-styled form by its own-form pollen, and by that 

 of the short-styled ; and the stigma of the short-styled 

 form by its own-form pollen, and by that of the long- 

 styled. The fertilisation of either form with pollen from 

 the other form may be conveniently called a legitimate 

 union, from reasons hereafter to be made clear ; and that 

 of either form with its own-form pollen an illegitimate 

 union. I formerly applied the term " heteromorphic " 

 to the legitimate unions, and " homomorphic " to the 

 illegitimate unions ; but after discovering the exist- 

 ence of trimorphic plants, in which many more unions 

 are possible, these two terms ceased to be applicable. 

 The illegitimate unions of both forms might have been 

 tried in three ways ; for a flower of either form may be 

 fertilised with pollen from the same flower, or with that 

 from another flower on the same plant, or with that 

 from a distinct plant of the same form. But to make 

 my experiments perfectly fair, and to avoid any evil 

 result from self-fertilisation or too close interbreeding, 

 I have invariably employed pollen from a distinct 

 plant of the same form for the illegitimate unions of 

 all the species; and therefore it may be observed that 

 I have used the term " own-form pollen " in speaking 

 of such unions. The several plants in all my experi- 

 ments were treated in exactly the same manner, and 

 were carefully protected by fine nets from the access of 

 insects, excepting Thrips, which it is impossible to ex- 

 elude. I performed all the manipulations myself, and 

 weighed the seeds in a chemical balance ; but during 



