LIMIT OP PHYSIOLOGICAL WATER 47 



Case II {Deficient in light, other conditions normal.) 



Physical Record. 



Average air temperature 74° 



Average relative humidity 72% 



Average soil temperature 66° 



Average soil moisture 14.6% 



Average maximum light 0.5% 



RESULTS NON-AVAILABLE PLANT 



WATER WATER 



Average 9 plants 9.0% 41.5% 



These give the wide difference of 4.2 per cent in the 

 amount of water non-available for the use of the plant. Such 

 intense shade brought about a pathological condition in Case 

 II. 



The plants in plots P-I and P-II were under precisely 

 the same physical conditions excepting that of soil water. 

 They received several times more light than those in the 

 shade in Case II. The latter were in a diseased condition 

 and would never have borne fruit had they been permitted 

 to live. The former adapted themselves in a greater or less 

 degree to their conditions and showed every indication of 

 fruiting had they been allowed to continue their existence. 



It cannot be definitely determined when a plant ceases to 

 be able to adapt itself to its conditions, that is, just when a 

 plant passes from a normal to a pathological condition. If 

 a plant is changed from a sunny situation into one of con- 

 stant shade there can be little doubt that it suffers from the 

 effects for a time, and during this period must be in a path- 

 ological condition. If the shade is not too intense it may so 

 adapt itself to its conditions as to be able to perpetuate its 

 species even when its condition is not one of health. 



When one plant is unable to witharaw as much water 

 from the soil during drought as another of the same spceies 

 situated under different air or light conditions, it cannot be 

 safely maintained that this is because the one in the less 

 favorable condition has adapted itself to its new habitat by 

 a change of structure. Although it has a modified structure, 



