Chap. X. 



SEXUAL RELATIONS OP TLANTS. 



415 



gamous they would be practically diclinous.* As far 

 as anemophilous plants are concerned, we know that 

 they are apt to have their sexes separated, and we can 

 see that it would be an unfavourable circumstance for 

 them to bear their flowers very close to the ground, as 

 their pollen is liable to be blown high up in the air ; t 

 but as the culms of grasses give sufficient elevation, 

 we cannot thus account for so many trees and bushes 

 being diclinous. We may infer from our previous 

 discussion that a tree bearing numerous hermaphrodite 

 flowers would rarely intercross with another tree, 

 except by means of the pollen of a distinct individual 

 being prepotent over the plant's own pollen. Now the 

 separation of the sexes, whether the plant were anemo- 

 philous or entomophilous, would most effectually bar 

 self-fertilisation, and this may be the cause of so many 

 trees and bushes being diclinous. Or to put the case 

 in another way, a plant would be better fitted for 

 development into a tree, if the sexes were separated, 

 than if it were hermaphrodite ; for in the former case 

 its numerous flowers would be less liable to continued 

 self-fertilisation. But it should also be observed that 

 the long life of a tree or bush permits of the separation 

 of the sexes, with much less risk of evil from impreg- 

 nation occasionally failing and seeds not being pro- 

 duced, than in the case of short-lived plants. Hence 

 it probably is, as Lecoq has remarked, that annual 

 plants are rarely dioecious. 



* With respect to the Proteacese 

 of Australia, Mr. Bentham re- 

 marks (' Journal Linn. Soc. Bot.' 

 vol. xiii. 1871, pp. 58, 64) on the 

 various contrivances by which the 

 etigma in the several genera is 

 screened from the action of the 

 pollen from the same flower. For 

 instance, iu Synaphea " the stigma 



is held by the eunuch (i.e., one 

 of the stamens which is barren) 

 safe from all pollution from her 

 brother anthers, and is preserved 

 intact for any pollen that may be 

 inserted by insects and other 



f Kerner, ' Schutzmittel 

 Pollens/ 1873, p. i. 



dea 



