Chap. XVIII. 



STERILITY. 



171 



gous with the foregoing could be given ; for instance, some kinds of mosses 

 and lichens have never been seen to fructify in France. 



Some of these endemic and naturalised plants are probably rendered 

 sterile from excessive multiplication by .buds, and their consequent inca- 

 pacity to produce and nourish seed. But the sterility of others more 

 probably depends on the peculiar conditions under which they live, as in 

 the case of the ivy in the northern parts of Europe, and of the trees in 

 the swamps of the United States ; yet these plants must be in some 

 respects eminently well adapted for the stations which they occupy, for 

 they hold their places against a host of competitors. 



Finally, when we reflect on the sterility which accompanies 

 the doubling of flowers, — the excessive development of fruit, 

 — and a great increase in the organs of vegetation, we must 

 bear in mind that the whole effect has seldom been caused at 

 once. An incipient tendency is observed, and continued selec- 

 tion completes the work, as is known to be the case with our 

 double flowers and best fruits. The view which seems the most 

 probable, and which connects together all the foregoing facts 

 and brings them within our present subject, is, that changed 

 and unnatural conditions of life first give a tendency to sterility ; 

 and in consequence of this, the organs of reproduction being no 

 longer able fully to perform their proper functions, a supply of 

 organised matter, not required for the development of the seed, 

 flows either into these same organs and renders them foliaceous, 

 or into the fruit, stems, tubers, &c, increasing their size and 

 succulency. But I am far from wishing to deny that there 

 exists, independently of any incipient sterility, an antagonism 

 between the two forms of reproduction, namely, by seed and 

 by buds, when either is carried to an extreme degree. That 

 incipient sterility plays an important part in the doubling of 

 flowers, and in the other cases just specified, I infer chiefly from 

 the following facts. When fertility is lost from a wholly dif- 

 ferent cause, namely, from hybridism, there is a strong ten- 

 dency, as Gartner 114 affirms, for flowers to become double, and 

 this tendency is inherited. Moreover it is notorious that with 

 hybrids the male organs become sterile before the female 

 organs, and with double flowers the stamens first become foli- 



114 ' Bastarderzeugung,' s. 565. Kol- one single and the other double are 

 reuter (' Dritte Fortsetzuog,' s. 73, 87, crossed, the hybrids are apt to be 

 119) aLo shows that when two species, extremely double. 



