METHODS OF POLLINATION. 35 



the offspring in all sorts of ways, as to heights and 

 fertility. He generally found that with the first two 

 or three generations the " crossed " plant beat the 

 " self-fertilized." 



But he rarely continued the experiments for a 

 sufficient number of years. For crossing is a temporary 

 stimulus ; and after a few years the continually self- 

 fertilized gradually gain upon the intercrossed, and then 

 far outstrip them in fertility. 



Florists corroborate this result. By constantly 

 crossing to procure finer flowers, after a time fertility 

 rapidly decreases, and it is often next to impossible to 

 get the finest flowers to set any seed at all. Just as 

 pigeon-fanciers say the best pigeons always die in 

 the nest, so a certain florist lost his whole stock of 

 valuable primulas from this cause. 



On the other hand, self-fertilizing weeds as Ground- 

 shell, Shepherd's-purse, Black Solanum, Chickweed, 

 etc., are sturdy little plants, terribly prolific, and an 

 intolerable nuisance in the warden. 



