CHAP. XII. GENERAL RESULTS. 471 



The offspring from a union between plants of the same 

 form are more or less sterile, like hybrids, and have 

 their pollen in a more or less aborted condition ; and 

 some of the seedlings are as barren and as dwarfed as 

 the most barren hybrid. They also resemble hybrids in 

 several other respects, which need not here be specified 

 in detail, such as their sterility not corresponding 

 in degree with that of the parent plants, the unequal 

 sterility of the latter, when reciprocally united, 

 and the varying sterility of the seedlings raised from 

 the same seed-capsule. 



We thus have two grand classes of cases giving results 

 which correspond in the most striking manner with 

 those which follow from the crossing of so-called true 

 and distinct species. With respect to the difference 

 between seedlings raised from cross and self fertilised 

 flowers, there is good evidence that this depends alto- 

 gether on whether the sexual elements of the parents 

 have been sufficiently differentiated, by exposure to 

 different conditions or by spontaneous variation. The 

 manner in which plants have been rendered hetero- 

 styled is an obscure subject, but it is probable that the 

 two or three forms first became adapted for mutual 

 fertilisation, that is for cross-fertilisation, through the 

 variation of their stamens and pistils in length, and 

 that afterwards their pollen and ovules became co- 

 adapted ; the greater or less sterility of any one form 

 with pollen from the same form being an incidental 

 result.* Anyhow, the two or three forms of hetero- 

 styled species belong to the same species as certainly 

 as do the two sexes of any one species. We have 

 therefore no right to maintain that the sterility of 

 species when first crossed and of their hybrid offspring, 



* This subject has been discussed in my 'Different Formt of 

 Flowers &o.,' pp. 260-268. 



