AGRICULTURAL SCIENCE AT THE ST. LOUIS MEETING. 539 



moisture ))y transpiration, but may conserve or even increase tlie mois- 

 ture by their action as wind-breaks, thus preventing evaporation, and 

 also b}" the absorptive action of the added humus. The}' ma}' also 

 prevent loss of heat from the soil and deep freezing. The amount of 

 transpiration of plants imder actual field conditions is not known and 

 needs systematic study. Cover crops may be classified in two groups, 

 according as they are winterkilled or not, and their value depends in 

 a considerable degree upon the class to which the}' belong. In experi- 

 ments in Neljraska it was found that rye has a drying efl'ect on the 

 soil and that the most successful cover crops are those which are 

 killed by the frost. The roots of fruit trees are hardier in a soil con- 

 taining 20 per cent of moisture than in one containing 15 per cent. 

 The effect of cover crops in preserving this moisture is therefore very 

 important. Their effect upon soil temperatures is not well understood, 

 but the soil is protected from deep freezing by their presence, espe- 

 cially through their action in holding snow upon the ground. In a 

 comparative tost there was 18 in. of snow on ground occupied by cover 

 crops, while check plats showed only 2 in. Dry soils were found to 

 freeze and thaw much more rapidly than wet soils. Cover crops 

 should stand erect. Millet is considered as the best cover crop in 

 Nebraska. 



In the symposium on shading L. C. Corbett discussed the practice 

 in a general manner, reviewed the work which has been done in .shad- 

 ing tobacco, citrus fruits, studies of humidity and temperature of the 

 soil, and the effect on plant foliage, earliness of crops, and decrease in 

 yields. It was argued that the practice is best applicable to plants 

 grown for foliage. B. M. Duggar called attention to the fact that 

 many studies on etiolation have been published, but few studies on 

 shading from a horticultural standpoint. In general there appears to 

 be more acid in plants under shade and the reserve materials are 

 greatly diminished. Attention was called to the desirability of carry- 

 ing on quantitative work to determine the amount of transpiration of 

 plants. 



The subject of shading strawberries was presented by V'. A. Clark 

 and O. M. Taylor. Varieties of strawberries were grown on difierent 

 soils. In some varieties the yield was increased, in others diminished. 

 When a heavy form of cheese cloth was used in shading in a test of 16 

 varieties, the yield was diminished 13 to 70 per cent. 



P. H. Rolfs discussed the subject of shading pineapples and citrus 

 fruits. This practice was first tested in the South as a protection 

 against frost. It has been found that on light Florida soils shading 

 doubles the amount of soil moisture. Orange trees require consider- 

 able light, but shading prevents transpiration and thus partly com- 

 pensates for the diminished light. \n shading the shoots grow longer. 



17<)72— No. 6— 01^ 2 



