24 STUDIES IN THE VEGETATION OF THE STATE 



may be greater. Turgid plants growing in sand have the 

 highest per cent, of water. This must be due to the lack 

 of nutrient salts in quartz sand. The plants in this soil 

 grew the slowest and were the least vigorous in appearance. 

 Those growing in humus were by far the most vigorous in 

 size and appearance, yet had the lowest per cent of water. 

 The series of soils taken in order of plant vigor from the 

 highest to the lowest is as follows: humus, loess, clay, 

 saline, loam, sand. The fact that parasitic fungi attacked 

 the roots of the plants to a greater extent in some soils than 

 in others slightly vitiates the results obtained. The plants 

 of Zea in Case II were attacked by Fmarium but the results 

 from the diseased plants were not included in the table. 

 One thing is strongly indicated, namely, that the plant which 

 is most vigorous does not necessarily contain the most water. 

 In fact, the least vigorous plants were the most watery, for 

 example, those growing in the shade in Case II. 



2. The Amount of Water in Plants Wilting Strongly under 

 Measured Physical Conditions, and the Corresponding Amount in 

 the Soil. 



The cause of the wilting or drooping of the aerial portions 

 of the plant is the lack of cell turgidity due to a loss of 

 water. When the protoplasm loses water, it ceases to exert 

 a pressure upon the cell-walls and gradually shrinks in bulk 

 allowing the whole superstructure of the softer portions of 

 the plant to collapse. Any physical factor that increases 

 the evaporation from the leaves to such an extent that the 

 roots cannot furnish a compensatory supply is certain to 

 bring about this condition. Plants growing in natural con- 

 ditions often wilt considerably during the hotter and dryer 

 portion of the day and recover their turgidity during the 

 cooler and moister hours of the night. Most plants seem 

 able to withstand a succession of such experiences without 

 serious injury if timely rains intervene. 



Although many observations were made upon the relative 

 amount of water in wilting plants and in the soils in which 

 they grow, but one experiment was conducted with this end 



