126 



The Plant World 



In a brief paraphrase of the principal|ideas presented in this 

 sketch it is to be said that Darwinism, which has so profoundly 

 affected human thought, and is without parallel so far as impor- 

 tance of conclusions and force of suggestion are taken into ac- 

 count, was the climax of the purely observational method of 

 advancing knowledge. It came at a time when biological 

 thought was ripe for a change of attitude and method of dealing 

 with natural phenomena. Its great author, together with other 

 leaders in biology, passed almost wholly to experimentation 

 in the discovery, demonstration and confirmation of the prin- 

 ciples underlying the action of the constituency of the organic 

 world. This method was used to the fullest extent, first in 

 physiological inquiry, in the calibration of functional perform- 

 ances and was later applied to ontogenetic development and 

 the interpretation of form, so that even now taxonomic and 

 phyletic generalizations lean upon its results for support. 

 Genetics, descent and heredity escaped more slowly from the 

 domination of illusive speculations and dogmatic philosophy, 

 but now in these, as in practically all branches of human thought, 

 we are no longer content with casual and hazardous arrangements 

 of facts to lit preconceived theories; with unrestrained, meta- 

 physical interpretations of nature, but demand progression by 

 experience and the foundation of generalizations concerning 

 evolution upon known causes, appreciable mechanisms and 

 movements of ascertained direction. 



Extensive fields of research lie without the domain of ex- 

 perimentation, yet the data gleaned from them must be put to 

 the test of comparison with results analytically obtained. In 

 a direct study of genetics we have at our command the pedigree 

 culture; the conception of unit characters; some facts and a 

 practicable theory as to the mechanism of heredity, and the 

 physical basis of inheritance; a better knowledge of the nature 

 and causes of variability, due to the use of statistical methods, 

 with a realization of the importance of continuous and discon- 

 tinuous variations; the power of inducing certain departures 

 by the use of compounds or climatic factors; much evidence, 

 chiefly of a palaeontological character, as to the definitness of 

 variations; a comprehension of the relations of environic factors 

 to germ plasm and soma and some important results in selection 



