CHAPTER IX 

 THE ORIGIN OF NEW FORMS 



200. The law of evolution. Evolution is the production of 

 a new plant form out of an existing one. It is commonly spoken 

 of as the origin of species, but this expression is far from exact. 

 All plant groups, forms, varieties, species, genera, etc., regardless 

 of their rank, are products of evolution. The term species, 

 moreover, has become so vague that it no longer has definite 

 meaning from the standpoint of evolution. Properly speaking, 

 the latter is the origin of all new forms. The existence of such 

 a universal process is now beyond question. The exact ways 

 in which new forms arise and the factors which control their 

 origin are still imperfectly known. Evolution has scarcely entered 

 the experimental stage. There has been a surplus of works and 

 papers upon this subject, but with few exceptions they have added 

 nothing to our real knowledge of it. 



201. Stability and plasticity. Evolution is the process in which 

 organisms are changed by the immediate or remote action of their 

 environment. The exact connection between many changes in 

 plants, for example, and their habitat has not yet been made, 

 owing to the extremely small amount of experimental study. 

 The feeling that all changes can be traced sooner or later to the 

 factors of the habitat arises from the belief that every form has 

 descended from the primitive protoplasm, solely in consequence 

 of changes wrought in the latter by the halntat. The most con- 

 vincing evidence in favor of this belief, which naturally can never 

 be proved or disproved, is found in the fact that every form used 

 for experiment can be changed in response to changing factors. 

 Consequently we are justified in assuming as a working h>^^othesis 

 that all plants can be changed by means of the habitat. To 



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