SPECIES LISTS— NON-AVAILABLE WATER 69 



SPECIES LISTS— NON-AVAILABLE WATER. 



At the close of this explanatory chapter are two lists of 

 species, the first giving the average results from plants 

 grown under the full light in the plant house, and the sec- 

 ond a list of results from plants in the fields about Lincoln. 

 In growing a large number of plants, except in the compar- 

 ative plots, it was impossible to keep the soil equally moist 

 in all the pots, the amount of water in the soil averaging 

 from 10 to 25 per cent. As a result some of the pots with 

 smaller plants maintained a higher per cent of soil moisture 

 than others with larger plants. The conditions of air and 

 soil temperature were quite uniform. Some of the results 

 obtained from a few plants are placed in the ' ' Species Sheets" 

 immediately following the "Species Lists". Here are given 

 the results of work from both plant house and laboratory. 

 These results vary as might be expected, since the plants 

 are grown in different physical conditions as regards soil, 

 air, temperature and light. One slight source of variation 

 is the injuries received by many plants from the punctures 

 of small insects infecting the plant house; another is that 

 caused by parasitic root fungi. The average results of plant 

 house and laboratory plants is somewhat higher than that 

 for plants in their natural habitat, yet not so great as might 

 be expected, when the greater humidity, the deficient light 

 of the plant house and the effects of the injuries from insects 

 and parasites are taken into consideration. The plants in 

 the field are also subject to injuries from insects and fungi, 

 and in addition are more apt to suffer mechanical injuries 

 from the wind. Where the results seemed to depart widely 

 from the limit of plants of similar habitat but different 

 species, the error was directly traceable to the mechanical 

 or structural injuries received by the plants before or dur- 



