eo LUTHER BURBANK 



Cambridge, England; published by the Univer- 

 sity Press : 



It is a remarkable thing that apart from the funda- 

 mental attributes of living matter — assimilation, irritability, 

 growth, and so forth — no single character is so widely dis- 

 tributed as sex ; it occurs in some form in every large group 

 of plants and animals from the highest to the lowest and 

 yet of its true nature and meaning we have hardly a sus- 

 picion. Other widely distributed characters have obvious 

 functions; of the real function of sex we know nothing, 

 and in rare cases where it seems to have disappeared, the 

 organism thrives to all appearances just as well without 

 it. And in many other cases, especially in plants, where 

 sex is definitely present, it may apparently be almost or 

 quite functionless, as for example, in the considerable num- 

 ber of plants which are habitually grown from grafts or 

 cuttings, and in which the fertile seeds are never set. It 

 is of course impossible to say with confidence that such 

 "asexual" reproduction can go on quite indefinitely, but the 

 evidence formerly adduced that continued vegetative repro- 

 duction leads to degeneration has been shown to be of 

 doubtful validity. Sex, therefore, although it is almost 

 universally found, cannot be said with certainty to be a 

 necessary attribute of living things, and its real nature re- 

 mains an apparently impenetrable mystery. 



Now, after more than fifty years of practical 

 experiments in the evolution of new plant forms, 

 the purpose of sex seems too plain even to need 

 much explanation, much less any doubt what- 

 ever as to its purpose in the scheme of things. 



