42 STUDIES IN THE VEGETATION OF THE STATE 



When a plant is suddenly transferred from moist condi- 

 tions to xerophytic, the rapid change prevents the plant from 

 adapting itself at all to its conditions, and death takes place 

 quickly. This was especially true of the two plots for which 

 data are just given. The plants in the laboratory were all 

 dead by the time the first in the plant house began to die, 

 the average time of drying up was twice as long for the plant 

 house. The difference in the averages is quite pronounced. 

 The plants transferred to the xerophytic laboratory died at 

 an increase of 1.4 per cent in the limit. This indicates 

 that periods of drought following quickly after moist weather 

 and good growing conditions may injure plants more 

 quickly in the fields than a more gradual change from wet 

 to dry weatJaer. 



4. Tn.e Effect of Increased or Decreased Soil Moisture during 

 the Growing Period. 



If a xerophyte is placed under the conditions of a meso- 

 phyte, or if the latter is placed under semi-hydrophytic con- 

 ditions, in either case the plant must adapt itself to the new 

 conditions or become unhealthy and die. Such a plant can 

 rarely fully adapt itself in one generation but manages to 

 exist and reproduce itself though in a condition of lowered 

 vitality. The same thing is true where the order is reversed 

 and the hydrophyte and mesophyte are put under the effect 

 of a lower per cent of soil moisture than that to which they 

 are accustomed. 



The following data were taken from plants growing in the 

 plant house in the same physical conditions, with the 

 exception of a difference in the water content of the soil. 

 The results indicate the effect of increasing the water in 

 the soil beyond the amount to which the plant has been 

 accustomed. Most of these plants are mesophytes but 

 several have xerophytic tendencies. The latter show the 

 greatest differences. 



