522 EXPERIMENT STATION RECORD. 



occur. It appeared in general that the soil was dried out appreciably by root 

 absorption in the neighborhood of the roots, and that this partial desiccation 

 usually lagged considerably behind its primary cause, rise in transpiration rate. 

 This lag rendered the attraction of the soil for water noticeably high for some 

 time after the transpiration rate had attained its low night value. To what 

 degree the lag occurred in the plant and to what degree in the soil intervening 

 between roots and the irrigator cup lias not as yet been determined. 



A bibliography is given. 



Hourly transpiration rate on clear days as determined by cyclic environ- 

 mental factors, L. J. Bbiggs and H. L. Shantz {U. S. Dept. Agr., Jour. Agr. 

 Research, 5 {1916), No. H, pp. 583-650, pis. 3, figs. 22).— In continuation of 

 other studies on water requirements of plants (E. S. R.. 32, p. 127), the authors 

 have undertaken a series of transpiration measurements with a view to deter- 

 mining the relative influence of various environmental factors on the transpira- 

 tion of different plants. The methods and apparatus used were similar to those 

 previously described (E. S. R., 34, p. 226). The present paper deals with 

 measurements of transpiration at Akron, Colo., on clear days in relation to 

 environmental factors, the plants used being wheat, oats, rye, sorghum, alfalfa, 

 and amaranthus. In addition to determining transpiration, records were made 

 of radiation intensity, air temperature, depression of the wet-bulb thermometer, 

 evaporation, and wind velocity. 



Composite graphs are presented to show the mean hourly transpiration rate 

 for each of the plants considered. On the basis of the form of the curves, the 

 transpiration graplis may be gi-oupwl into two classi's having characteristic 

 features. The cereals show marked changes in the form of the transpiration 

 graph in the forenoon, unaccompanied by corresponding changes in the environ- 

 mental factors. On the other hand, the forage plants and amarantlms give little 

 or no indication of such a change. The flattening of the graphs in case of the 

 cereals is believed to be due to some change in the plant, resulting in a reduction 

 in the transpiration rate below what would be expected from the form of the 

 curve during the early morning hours. 



The hourly transpiration rate of cereals on clear days increased steadily, 

 though not uniformly, from sunrise to a maximum value, usually reached 

 between 2 and 4 p. m., after which it fell rapidly to the night level. In the 

 case of sorghum, alfalfa, and amaranthus, the transpiration curves were some- 

 what more symmetrical, reaching their maximum between noon and 2 p. m., 

 after which they fell approximately with the radiation. Wlien all the mean 

 hourly values were expressed as a percentage of the maximum, the radiation 

 intensity was found to rise in advance of transpiration and to fall either in 

 advance of transpiration or with it, depending upon the plant consideretl. From 

 this it is considered that radiation may be looked upon as the primary causative 

 factor in these cyclic changes. 



If the environmental factors are considered as independent, tlieir relative 

 influence on transpiration, it is said, may be determined by the method of least 

 squares. 



Notes on plant chemistry. P. Q. Kef.g.\x (Chrm. .Yrir.s. Jll (1015), Xo. 2899, 

 pp. 289, 290). — Tliis is a discussion of rtcridiiim aiiiiilinimi, Ljichnis dioiva, 

 Hifpericutn perforatum, and Nymphcca alba, dealing principally with the chemi- 

 cal constituents of these plants and more or less with their anatomical struc- 

 tures, modes of life, habitats, and products. 



Carbohydrate transformations in s'weet potatoes. H. IlAssEi.nniNG and L. A. 

 Hawkins {U. S. Dcpt. Agr., Jour. Agr. Research. 5 (1915), No. 13. pp. 545- 

 560). — In continuation of studies of carbohydrate transformation (E. S. R., 32. 



