IN THE VEGETABLE KINGDOM 49 



by cultivation without the intervention of selection. 

 We are justified in inferring, although Darwin does not 

 make this point perfectly clear, that the wild plants 

 which seed freely in cultivated soil are, as a rule, less 

 fertile at first than in a wild state. 



He goes on to say : " Too much manure renders some 

 kinds utterly sterile, as I have myself observed. The 

 tendency to sterility from this cause runs in families ; 

 thus, according to Gartner, it is hardly possible to give 

 too much manure to most Graminse, Cruciferse and Legu- 

 minosse, whilst succulent and bulbous-rooted plants are 

 easily affected. Extreme poverty of soil is less apt to 

 induce sterility, but dwarfed plants of Trifolium minus 

 and repens grown on a lawn often mown and never 

 manured were found by me not to produce any 

 seed." i 



Observe that the plants mentioned as being difficult 

 to reduce in their fertility by heavy manuring are pro- 

 pagated by seed, or cultivated for a heavy yield of seed 

 in a rich soil. We must expect considerable variation 

 between different varieties in their response to a given 

 combination of conditions, as they will represent different 

 degrees of adaptation. 



" Many of our most valuable fruits, although consisting 

 in a homological sense of widely different organs, are 

 either quite sterile, or produce extremely few seeds. This 

 is notoriously the case with our best pears, grapes and 

 figs, with the pineapple, banana, breadfruit, pomegranate, 

 azerole, date-palms and some members of the orange 

 tribe. Poorer varieties of these same fruits either habitu- 

 ally or occasionally yield seed. Most horticulturists look 

 at the great size and anomalous development of the 

 fruit as the cause and sterility as the result, but the 



1 Variation of Animals and Plants under Domestication, chap, xviii. 



4 



