BUEEAU OF PLANT INDUSTRY. 159 



Virginia. These deposits were used very extensively to improve the 

 soil for more than a generation before the Civil War. Greenhouse 

 experiments with wheat and red clover showed that although the 

 greensand found in these deposits is slowly soluble in water under 

 laboratory conditions, it is acted upon by the roots of plants and by 

 other factors in the soil sufficiently to fr'ee the potassium required 

 to make an excellent growth during the early life of the plant, the 

 period during which potassium absorption is most active. 



DROUGHT RESISTANCE OF CROPS. 



During the year work on the water requirement of crops was con- 

 tinued at Huntley, Mont., Yuma, Ariz., and Chula Vista, Cal. The 

 results" indicate that the consumption of water during the winter 

 period in the Southwestern Desert region is less than in the case of 

 the same crop plants when grown during the summer period in the 

 Great Plains region. A comparatively great crop return is obtained 

 in localities where the temperature conditions permit the utilization 

 of water in winter. Where the water supply is very limited it can, 

 therefore, be utilized most economically by crops grown during the 

 cooler months of the year. It is believed that the results of these 

 investigations will be useful to irrigation engineers and agriculturists 

 by enabling them to estimate the quantities of water required by 

 different crops grown in different seasons of the year, especially in 

 places where actual irrigation experience with a particular crop has 

 not already been obtained. 



CROP-INDICATOR VALUE OF NATURAL VEGETATION. 



The methods worked out in these investigations have been put to 

 practical application in cooperation with the Land Classification 

 Board in classifying land under the grazing homestead act, and the 

 natural vegetation has proved to be a useful criterion for separating 

 land suitable for dry-land grain production from land which can 

 best be utilized for grazing. Investigations in the arid portions of 

 the Great Basin and the Southwest have progressed to the point 

 where the character of the land can be predicted very accurately from 

 the natural plant cover, and its value for dry farming and irrigation 

 agriculture can be inferred. 



LEAF-CUT, OR TOMOSIS, OF COTTON SEEDLINGS. 



Further observations have been made on this peculiar disorder that 

 very frequently lacerates and distorts the leaves of cotton seedlings 

 and not uncommonly results in the permanent deformity of the plants 

 by destroying the terminal bud. Thinning cotton too early invites 

 more injury from tomosis, on account of the greater exposure of the 

 young plants to extreme conditions. When cotton is thinned late the 

 crippled plants are easily recognized and removed, leaving only the 

 normal individuals. Lack of any indications of bacteria, fungi, in- 

 sects, or other parasites being responsible for leaf-cut left the causes 

 in doubt, but the seat of the disorder has now been traced to the oil 

 glands. The smallest lesions consist merely of a dead oil gland with 

 the adjacent cells penetrated and stained by dark material from the 

 dead gland. The oil ghmds are affected in advance of the other tis- 



