258 CHEMISTRY OF PLANT LIFE 



species. This adaptation of stage of growth to duration of daily 

 illumination must, therefore, be an evolutionary character of the 

 species. 



Hence, it appears that in many cases physiological adaptation 

 may be a direct response of the life-processes of the plant to the 

 daily length of photochemical stimulation which it receives from 

 solar light. But there is, as yet, no explanation of how this (or 

 any other) influence actually changes the vital processes of the 

 plant protoplasm so -as to bring about either a morphological adap- 

 tation of structure or a physiological adaptation of functions to 

 altered conditions of growth. 



CONCLUDING STATEMENTS 



Enough has been said to show how very inconclusive and 

 unsatisfactory is our knowledge of the phenomena known as 

 " adaptation." Even the nomenclature used by different scientists 

 to describe its various manifestations is confused and misleading. 

 For example, certain crops are said to be " adapted " (i.e., suited) 

 to certain types of soils, and vice versa; crops are said to be 

 "adapted " to given agricultural districts, etc. 



In this chapter, an attempt has been made to arrange in some 

 semblance of order some of the known manifestations of alteration 

 of fixed habits of growth of plants in response to changes of environ- 

 ment, and to point out some of the suggestions of possible explana- 

 tions of these phenomena which have been presented by different 

 investigators. 



This presentation cannot be considered as anything other than 

 an introduction to a field of study which is as yet almost entirely 

 unexplored, and, like all other unexplored territory, is full of 

 mysteries. If the study of this chapter serves to stimulate interest 

 in these mysteries and wonders of plant life, its purpose will 

 have been accomplished. 



