40 



STUDIES IN THE VEGETATION OF THE STATE 



PHYSICAL FACTORS 



Average temperature 



Averiige humidity 



Average soil temperature 



Average soil moisture 



Average maximum light 



Results 



Average limit of physiological water. 

 Average water in dying plants 



Prom this experiment it is proven that humid air tends to 

 increase the size of the leaves, and to diminish the root sys- 

 tem of the plant. The plant begins to adapt itself to living 

 in such conditions, but in such a way that when the soil 

 dries out even with the air humidity unchanged, it is unable 

 to draw as much water from the soil as a plant growing 

 and dying in less humid atmosphere. The difference in non- 

 availabe water, 1.8 per cent., is quite marked. 



The effect of suddenly transferring plants raised in a 

 moist atmosphere to a dry one was shown by taking two col- 

 lections of potted plants raised in the plant house and trans- 

 ferring one of them to the xerophytic conditions of a dry 

 laboratory, leaving the other in nearly similar conditions of 

 light and heat in the more moist plant house. The follow- 

 ing data show the effect of true xerophytic conditions on 

 plants raised in a more humid atmosphere. 



Comparative Physical Record of Plant House and Laboratory. 



Average air temperature, planthouse 71° 



Average air temperature, laboratory 72° 



Average relative humidity, planthouse 62% 



Average relative humidity, laboratory S8% 



Average soil temperature, planthouse 68° 



Average soil temperature, laboratory 67° 



Average maximum light, planthouse 10.5% 



Average maximum light, laboratory 30.5% 



