328 BOTANICAL GAZETTE [april 



bulb depression, 0.88; with temperature, 0.71; with radiation, 0.65; and 

 with wind velocity, 0.22. These serve to emphasize the close relation of 

 transpiration to humidity and evaporation and the comparatively slight influ- 

 ence of wind velocity. 



It is also interesting to note that during a 10-day period of maximum trans- 

 piration the daily loss of water ranged from 6 to 9 times the dry weight of the 

 crop for millets and corn, from 12 to 16 times for the small grains, and up to 

 36 to 56 times for alfalfas. During the same 10-day period the annual crop 

 plants lost about one-fourth of the total water transpired during the entire 

 season. The transpiration of the different crop plants per unit area of plant 

 surface shows less variation than the transpiration per unit of dry weight, 

 hence the greater efficiency shown by certain plants in the use of water 

 seems to be due more to a reduction in plant surface than to a reduction of 

 transpiration per unit area of surface. Various other comparisons make 

 this a valuable report for both the botanical and the agricultural 

 investigator. 



Another investigation undertaken with a view to economic application of 

 results shows scientific merit of a high order and is comparable in methods and 

 results with that just reviewed. In it Kiesselbach 12 has limited his research 

 to corn grown under conditions very closely approximating those of crop pro- 

 duction. A portion of the experiments was devoted to the development of a 

 satisfactory technique, and errors of former experimenters due to the use of 

 immature plants and small quantities of soil were pointed out. It is impossible 

 to summarize the many data, but it is interesting to note the agreement with 

 the results of Briggs and Shaxtz in the very large proportion of total water 

 used by the plant, which is lost during a comparatively short period of maximum 

 transpiration. A rather surprising result is that it was found that corn plants 

 grown for 2 months in a humid greenhouse exhibited no different transpiration 

 rate per unit leaf area when transferred to dry conditions than took place from 

 plants continuously grown under dry conditions. Further it appears that 

 while there were considerable variations in the different varieties in regard 

 to thickness of leaf and epidermis, and also in number of stomata per unit of 

 leaf area, there was no consistent correlation between these structural features 

 and the transpirational rate per unit of dry matter produced. In spite of this 

 it was found that the water requirement of different varieties differed to a 

 marked degree, suggesting that drought-resistant strains may be selected. It 

 also developed as an important result of the investigation that water economy 

 is greatest with neither an excessive nor a deficient soil moisture supply, and 

 further that increasing fertility by the application of fertilizers resulted in 

 still greater water economy. 



12 



Kiesselbach, T. A., Transpiration as a factor in crop production. Research 



/ r — l A M. 



Bull. no. 7, Neb. Agric. Exp. Sta. pp. 214. pis. 4. figs. 24. 19 16. 







