164 HETEROSTYLED TRBIOEPHIC PLANTS. CHAP. IV. 



balanced the higher efficiency of the female organs 

 in this form with the lesser efficiency and lesser size 

 of its two kinds of pollen-grains. The whole case 

 appears to me a very curious one. 



It may be observed in Tables 23 to 25 that some 

 of the illegitimate unions yielded during neither year 

 a single seed ; but, judging from the long-styled plants, 

 it is probable, if such unions were to be effected re- 

 peatedly by the aid of insects under the most favour- 

 able conditions, some few seeds would be produced in 

 every case. Anyhow, it is certain that in all twelve 

 illegitimate unions the pollen-tubes penetrated the 

 stigma in the course of eighteen hours. At first I 

 thought that two kinds of pollen placed together on 

 the same stigma would perhaps yield more seed than 

 one kind by itself ; but we have seen that this is not 

 so with each form's own two kinds of pollen ; nor is it 

 probable in any case, as I occasionally got, by the use 

 of a single kind of pollen, fully as many seeds as a 

 capsule naturally fertilised ever produces. Moreover 

 the pollen from a single anther is far more than suffi- 

 cient to fertilise fully a stigma ; hence, in this as with 

 so many other plants, more than twelve times as much 

 of each kind of pollen is produced as is necessary to 

 ensure the full fertilisation of each form. From the 

 dusted condition of the bodies of the bees which I 

 caught on the flowers, it is probable that pollen of 

 various kinds is often deposited on all three stigmas ; 

 but from the facts already given with respect to ' 

 the two forms of Primula, there can hardly be a 

 doubt that pollen from the stamens of corresponding 

 length placed on a stigma would be prepotent over 

 any other kind of pollen and obliterate its effects, 

 even if the latter had been placed on the stigma 

 some hours previously. 



