The Mutation of Structure 209 



periment, that the form and structure of 

 the organs of plants are due to the immediate 

 response of living protoplasm to the influence 

 of the environment, and that it, or rather the 

 nucleus, builds up just those cells and tissues 

 which are conformable to the conditions of life. 

 Then after a few years they become hereditary, 

 and so fix the varietal or specific characters by 

 which they are distinguished. 1 



Mr. R. Ruggles Gates, when referring to this 

 subject, remarks that " it seems clear that the 

 plasticity and adaptability of organisms is one 

 of their main properties which has made evolu- 

 tion possible ; on the other hand, the ' tenacity ' 

 of heredity in perpetuating even small differ- 

 ences for long periods is essential if evolution 

 is to have any cumulative effect." ! 



The most reliable evidence as to the progres- 

 sive evolution of the animal kingdom is derived 

 from a study of their fossil remains in the vari- 

 ous geological strata of our own and other parts 

 of the world. The length of time these strata 

 have taken to form is an open question, but we 



1 The Journal of the Horticultural Society, August, 1915. 



2 The Mutation Factor in Evolution, pp. 221-321, by R. Ruggles 

 Gates. 



