304 Plant Life and Evolution 



Imperfect Individualization in Plants. One of 

 the greatest differences between the higher plants 

 and animals is the imperfect individuality of the 

 former compared with the more highly individual- 

 ized animal. We have already pointed out that an 

 oak is not an individual in the same sense that a 

 dog is. Each leaf-bud of the tree is a potential 

 individual, and the whole is a colony of like individ- 

 uals, rather than a single organism. We may cut 

 off a twig and plant it, and in time we shall have 

 another tree with all its parts, including flowers, 

 complete. There is here no question of the develop- 

 ment of sexual cells from similar germs in the 

 bud from which the tree grew, as there is abso- 

 lutely no trace of any flowering structures, and it 

 may be years before the new tree is large enough to 

 produce flowers. Moreover, the tree itself is, 

 properly speaking, asexual, sexuality being re- 

 stricted to the insignificant gametophytes, arising 

 respectively from the embryo-sac and the pollen- 

 spore. 



As the regeneration of the whole plant is possible 

 from a mere fragment of a bud or leaf, the germ 

 plasm, if it is present, must be distributed through- 

 out the somatic tissues, and therefore exposed 

 equally with them to the direct action of external 

 stimuli. This lack of individuality and great power 

 of regeneration, as well as the ready response to 

 stimuli of various kinds, makes it hard to discrimi- 

 nate between what may be considered purely onto- 



