12 STUDIES IN THE VEGETATION OF THE STATE 



The ratio of the sines obtained by dividing the latter by 

 the former is 65, that is, the light intensity on February 20 

 is 65 per cent of that of June 22. Again if the exposure 

 taken for 15 seconds in the morning of February 20 equals 

 in color that of 7 seconds at noon the same day, its intensity 

 is A of 65 per cent or 30.3 per cent. This method of 

 measuring light is not without error, but until we know 

 more of the nature and effect of the sun's rays, it is an ap- 

 proximate method of measuring those rays which are most 

 stimulating to the chlorophyll of the plant. 



The present investigation was suggested by Dr Clements, 

 under whose direction it has been carried out. The writer 

 is greatly indebted to Dr. Bessey and Dr. Clements for help 

 given in the course of experimentation. 



B. RESULTS OF INVESTIGATION 



The results of the series of experiments carried on in the 

 laboratory and the plant house from December, 1900, to June, 

 1901, are here considered in nearly the same order as that 

 of the outline given in the introduction. With these data 

 are incorporated the observations made in the fields near 

 Lincoln during a short period of excessive dryness in the 

 month of August, 1900. 



1. Water Gapadty of Soils. 



The water capacity of different soils varies directly with 

 their porosity, that is, with the air spaces they contain. This 

 is dependent upon the fineness of the soil particles. How- 

 ever, this is a subject that cannot be fully discussed in a 

 treatise of this nature. In order to know the comparative 

 amount of water, each of the six soils used in experimenta- 

 tion was subjected to the following experiment. Pulver- 

 ized soil of each kind, namely, sand, saline, loam, clay, loess 

 and humus, was placed in a drying oven at a temperature of 

 250° F. for 48 hours. Measured quantities of each were 

 weighed and placed in flat crystallizing dishes of approxi- 



