14^ PLANT LIFE. 



inherent in it tlial a new organism similar to tliat of which it 

 forms ])art may be produced. 



185. Adaptation. — -The interrelation of these powers, 

 their harmonious coworking and their variation to suit the 

 varj'ing conditions of the surrounding media (air, water, soil, 

 etc.), result in the proper performance of all the functions of 

 the plant. By means of these powers it is brought into re- 

 lation to the world about it, being adapted to other organisms 

 in whose company it lives, and enabled to withstand the 

 adverse conditions by which it is frequently threatened. 

 Every organism^ indeed, must adjust itself first to the e.xternal 

 physical conditions, and, second, to other organisms. (See 

 Part IV.) 



186. Physical conditions set limits upon the discharge of 

 its functions. Varying amounts of light, of heat, of moisture, 

 determine more or less rigidly how rapidly, or to what extent, 

 each function may be dischargecL Every function of the 

 plant is adapted, therefore, to an upper limit, the ma.xivnim , 

 and to a lower limit, the minimttm, above or below which 

 the performance of the function in ([uestion is impossible. 

 Between these limits tliere lies some point at wliich it pro- 

 ceeds most rapidly and effectively. This point is known as 

 the up/ i in urn. 



