CHAPTER XXXI. 



THE VARIETIES OF FERTILISATION. 



There are at least seven kinds of union : — (1) self-fertilisa- 

 tion, or the fertilisation of a pistil by the pollen from the 

 same flower (Autogamy) ; (2) crossing different flowers on 

 the same plant ; (3) crossing flowers on different plants of 

 the same stock ; (4) crossing flowers of different plants, but 

 of different stocks ; all the preceding being of exactly the same 

 form or variety of species ; (5) crossing varieties of the same 

 species ; (6) crossing different species of the same genus ; 

 (7) crossing different genera of the same order. 



When a knowledge of the floral sexes was first acquired, 

 the idea maintained was that hermaphrodite flowers were 

 specially adapted for self-fertilisation ; but it was, I believe, 

 Dean Herbert who first observed the importance of crossing, 

 in his work on the AmarylUdacefe (1836). He says, " I am 

 inclined to think that I have derived advantage from im- 

 pregnating the flowers from which I wished to obtain seeds 

 with pollen fi'om another individual of the same variety, or, 

 at least, from another flower rather than its own, and espe- 

 cially from an individual grown in a different soil or aspect." 



Mr. Darwin's work. On the Cross and Self Fertilisation 

 of Plants (1876), placed on a scientific basis, by means of 

 experimental verifications, the exact values of such crossings. 

 His conclusions, however, require considerable modifications. 



