FUNCTION.] STERILITY OF HYBRIDS. 251 



first stage than natural seedlings. Mr. Btdwill, in attempt- 

 ing crosses at Sydney, has also (as he informs me) raised 

 some with difficulty, which have invariably perished. In 

 these cases I apprehend that, although the affinity of the 

 juices is sufficient to enable the pollen to fertilise the ovule, 

 the stimulus is insufficient, the operation languid, and the 

 fertilisation weak and inadequate to give a healthy constitu- 

 tion. It has been generally observed that hybrid fertilisation 

 is slower than natural fertilisation, and that often a much 

 smaller number of ovules are vivified. The same cause pro- 

 bably operates in that respect : the affinity not being perfect, 

 the necessary ingredients are attracted by the pollen less 

 readily and insufficiently, and by many of the grains not 

 at all." 



