370 MEANS OP CROSS-FERTILISATION. Chap. X. 



Each of these lists contains by a mere accident the 

 same number of genera, viz., forty-nine.* The genera 

 in the first list include sixty-five species, and those in 

 the second sixty species ; the Orchideae in both being 

 excluded. If the genera in this latter order, as well as 

 in the AsclepiadsB and xipocynacea?, had been included, 

 the number of species which are sterile if insects are 

 excluded would have been greatly increased ; but the 

 lists are confined to species which were actually expe- 

 rimented on. The results can be considered as only 

 approximately accurate, for fertility is so variable a 

 character, that each species ought to have been tried 

 many times. The above number of species, namely, 

 125, is as nothing to the host of living plants ; but 

 the mere fact of more than half of them being sterile 

 within the specified degree, when insects are excluded, 

 is a striking one ; for whenever pollen has to be carried 

 from the anthers to the stigma in order to ensure full 

 fertility, there is at least a good chance of cross-fertili- 

 sation. I do not, however, believe that if all known 

 plants were tried in the same manner, half would be 

 found to be sterile within the specified limits ; for 



* The plants in these two lists anthers from the florets of one 



are entomophilous, or adapted for variety of wheat, which neverthe- 



fertilisation by insects, with the less produced a considerable num- 



exception of Zea and Beta, which ber of grains, being fertilised by 



are aneniophilous or fertilised by the surrounding plants. I state 



the wind. I may therefore here this fact, because Mr. A. S. Wil- 



repeat that, according to Eim- son concludes from his excellent 



pan ('Landwirth. Jarbuch,' B. vi. experiments ('Gardeners' Chroni- 



1877, pp. 192-233, and p. 1073), cle ' 1874, March 21, p. 375) that 



Rye is sterile if the access of wheat is invariably self-fertilised, 



pollen from other plants is pre- and no doubt it is so generally, 



vented ; whereas wheat and barley Mr. Wilson believes that all the 



are quite fertile under these condi- pollen shed by the exserted anthers 



tions. Rimpan states (p. 199) that is absolutely useless. This is a 



the different varieties of wheat be- conclusion which it would require 



have differently with respect to very rigid proof to make me to 



self and cross-fertilisation. He admit, 

 removed at an early ag3 all the 



