134 THE BIOLOGICAL PROBLEM OF TO-DAY 



depends; and, fundamentally, all that we term 

 biology the mode of life of organisms depends 

 upon the fact that different organisms react dif- 

 ferently towards the same external influences, and 

 these reactions differ not only qualitatively, but 

 also quantitatively, the finest gradations existing in 

 both cases.' 



For instance, in a plant-embryo roots are pro- 

 duced at the lower end under the influence of the 

 soil and of gravity. But it is upon the specific 

 nature of the protoplasm of different kinds of 

 plants that the special shape of the whole root 

 system depends : whether, for instance, the root 

 system ramifies superficially or strikes deep into 

 the soil; whether the rootlets grow quickly or 

 slowly ; in what fashion they fork, and whether or 

 no they form special structures like bulbs. 



Thus, even from my point of view, explanation 

 of the process of development requires the as- 

 sumption of the existence of different kinds of 

 germinal material in different kinds of organisms. 

 These germinal substances must be possessed of an 

 extraordinarily complex organisation, and must be 

 able to react in specific fashion that is to say, in 

 a fashion different in each species to all the 

 slightest internal and external stimuli encountered 

 from time to time as the organisation becomes 

 formed by cell division. 



In this sense I agree with what Naegeli says : 



' The egg-cells contain all actual specific char- 

 acters as truly as the adult organisms ; when they 

 exist in the condition of eggs, organisms are as 



