254 The Living Plant 



Moreover this condition of tone is more or less alterable under 

 continuous action of new conditions, and such tonic adjustment 

 to new conditions is commonly called acclimatization. We do not 

 yet know much as to the nature of the process, but there seems 

 little doubt that it is chemical in its nature, and represents a 

 process of chemical adjustment to the external conditions acting 

 as stimuli. An important phase of the same process is found in 

 the formation in the animal body of those special chemical sub- 

 stances called collectively " antibodies," which neutralize chemi- 

 cally the injurious substances formed in disease. Probably the 

 acquisition of tone and acclimatization are fundamentally similar 

 in principle, consisting in chemical alterations in the protoplasm 

 of such character that substances or features less efficient under 

 the prevailing conditions are replaced by others more efficient. 

 At least such seems to be the principle, though as to the details, 

 they are still with the future. 



As one views the various adjustive structures produced in 

 response to external stimuli (such as the knees of the Bald Cypress 

 just mentioned, the thicker epidermis of plants in dry places, 

 and so forth), one cannot but ask how these may be distinguished 

 from adaptive structures produced in the course of evolution; 

 and whether, after all, the two may not be fundamentally the 

 same thing. As to the first point, one cannot distinguish adjustive 

 from adaptive structures by any evidence except the test of 

 heredity, for adjustive structures are produced anew in each 

 generation only in response to certain stimuli and are absent 

 when the stimuli are lacking, while adaptive structures are pro- 

 duced regularly every generation quite regardless of the presence 

 or absence of the given stimulus. The only thing that is hereditary 

 in irritable adjustments is the capacity to make them. We have 

 an analogy in the different methods whereby republics and 

 monarchies are provided with rulers, for while the president of a 

 republic is often indistinguishable in mode of life and other 

 characteristics from a monarch, and may even surpass one in 



