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 garden. 



