204 Blossom and Seed 



And then, again, even when a plant bears perfect 

 flowers with both pistils and stamens, it not unfre- 

 quently happens that pollen from their own blossom, 

 or from another blossom on the same stalk, does not 

 suit the ovules. Some which are fertilized by the pollen 

 of their own blossom, close-fertilized, as it is called, do 

 well, and the seed is plentiful ; but in most cases it is 

 poor and even worthless. Sometimes the pollen from 

 a blossom on the same stalk actually has the effect of 

 poison, and when ?ipplied to the pistil-tip, causes it to 

 shrivel and decay, and makes the petals drop ; some- 

 times, again, it does neither good nor harm directly ; 

 it does not poison and it does not fertilize, but — ^which 

 is equally injurious — it prevents any other pollen re- 

 ceived afterwards from having any effect, so that in 

 either case the ovules are equally sure to shrivel. 

 Then, further, there are some plants, as, for instance, 

 certain of the passion-flowers, whose ovules cannot be 

 converted into seeds unless they receive pollen not 

 merely from another plant of the same species, but 

 from another plant of a difierent species — a passion- 

 flower, but a different species of passion-flower. 



Such, then, being some of the many arrangements by 

 which it is made difficult or impossible, fox ovules to be 

 fertilized by pollen from their own blossom, or from a 

 blossom on the same stalk, one must conclude that 

 there is some reason for them, and that seed is the 

 better for being cross-fertilized — fertilized, that is, by 

 pollen from another plant. And so, indeed, it proves ; 

 for if cross-fertilized and self-fertilized seeds be sown 

 together, it generally happens that the former grow up 

 so niuch the stronger as quite to overpower the rest. 



As a rule, then, cross-fertilized seed produces much 



