250 CHEMISTRY OF PLANT LIFE 



however, that some influence produces a fixity of habit of growth 

 and development which is almost inevitable in its operation. 



But while this unvarying habit of growth is one of the fixed 

 laws of plant life, there are occasional deviations from it. A 

 plant which, under normal conditions of growth, develops in a 

 certain fixed way, when exposed to unusual environmental condi- 

 tions, may, and often does, alter its habit of growth in what may 

 metaphorically be said to be an attempt to adjust itself to the new 

 conditions. Numerous examples of this phenomenon might be 

 cited. Certain algae, which grow normally hi water at a tem- 

 perature of 20 to 30 and which are killed if the temperature rises 

 above 45, have been grown for successive generations in water 

 the temperature of which has been gradually raised, until they 

 produce apparently normal growth in water the temperature of 

 which is as high as 78 ; also, certain types of algae normally grow 

 in the water of hot springs at temperatures of 85 to 90, and 

 others in arctic sea-water the temperature of which sometimes 

 falls to 1.8 and never rises above C. This phenomenon of 

 the adjustment of a species of plants to new conditions, which in 

 the case of farm crops is sometimes called " acclimatization," is of 

 common occurrence and is often utilized to economic advantage 

 in the introduction of new strains of crops into new agricultural 

 districts. Again, the normal development of plants may be 

 altered as the result of injury or mutilation. Thus, if the ear is 

 removed from the stalk of Indian corn, at any time after flowering, 

 there always results an abnormal storage of sucrose in the stalk, 

 instead of the normal storage of starch in the kernels. Similarly, 

 midsummer pruning of fruit trees generally results in the produc- 

 tion of abnormally large number of fruit buds on the remaining 

 limbs. Many other familiar examples of alteration of normal 

 development in response to, or as the result of, abnormal condi- 

 tions of growth might be cited. 



TYPES OF ADAPTATIONS 



To designate these different alterations of normal growth, 

 several different terms have been used. Among these, " adapta- 

 tion," " accommodation," and " adjustment " have been com- 

 monly used by different biologists. Sometimes these are used 

 interchangeably, and sometimes different terms are used to desig- 



