442 The Living Plant 



which purpose a common camelshair paint brush is admirable 

 and usually employed), and then press it against the desired 

 stigma, which is sticky and to which therefore the pollen adheres. 

 The difficulty in the process comes from the fact that undesired 

 pollen may also reach the stigma, and effect a wrong fertilization. 

 It is therefore necessary to prevent access of any pollen except 

 that deliberately placed upon the stigma by the experimenter. 

 Close pollination is prevented, in those plants which allow it, 

 by snipping off the stamens before the anthers are ripe; while 

 undesired cross pollination is prevented by use of a gauze, or thin 

 paper bag kept closely tied over the flower except at the moment 

 when the desired pollen is applied to the ripe stigma. The sight of 

 such bagged plants must be familiar to all those who have visited 

 agricultural experiment stations, and they are shown in figure 173. 



The reader will no doubt be surprised that in this discussion I 

 have laid no more stress upon cultivation, which surely, he will 

 say, does much improve plants. Cultivation consists in giving 

 to plants such conditions of space, nourishment, and freedom 

 from enemies as will permit them to develop to the highest degree 

 that their internal capacities allow. It produces, therefore, better 

 individuals and crops. But it does not produce better races, 

 because, as we know, the good effects of cultivation are chiefly 

 irritable responses whose results are never transmitted to the next 

 generation. Indirectly, however, cultivation does help in racial 

 improvement, for on the one hand all offspring are benefited by 

 greater physical health in their parents, and, on the other, with 

 greater physical vigor goes greater variability and tendency to 

 production of sports, — those foundations of the improvement of 

 races. Just as the best nourished animals play more vigorously 

 than the ill-nourished, so the best cultivated plants vary and sport 

 the most actively, — from very excess of physical vigor, no doubt. 



In my discussion of this subject thus far, I have made it an 

 aim, as elsewhere through this book, to exhibit the theory, so to 

 speak, of the subject. For this purpose I have had to separate 



