160 BOTANICAL GAZETTE [February 



An investigation upon a much larger scale, resulting in an abundance of * 

 data, is reported by Briggs and Shantz. 18 It was carried on at Akron, 

 Colorado, and the transpiration was determined by weighing plants potted in 

 sealed cans upon the automatic scales recently described by the same authors. 19 

 Solar radiation, wet-bulb depression, evaporation, air temperature, and wind 

 velocity were also measured, and the relationship between these physical factors 

 and transpiration was shown. The plants employed were wheat, oats, sorghum, 

 rye, alfalfa, and Amaranthns retrojlexus, the hourly rate throughout the entire 

 day being determined, the number of determinations ranging from 6 for 

 Amaranthus to over 40 for alfalfa. The resulting data are expressed in tables 

 and graphs which also serve to express their relationship with the physical 

 factors. Correlation coefficients and method of least squares are also used to 

 analyze these relationships and give some interesting results. Space permits 

 the citing of their final conclusion only, to the effect that their results agree 

 with those of other investigators that plants under conditions of high trans- 

 piration do not respond wholly as free evaporating systems, even if bountifully 

 supplied with water. It is interesting to note that none of the plants here 

 studied show the mid-day drop reported by Trelease and Livingston, by 

 Shreve, and by other observers at the Desert Laboratory. 



Muenscher 20 has used the method of determining water loss by weighing 

 and then making counts and measurements of the number and size of the 

 stomata of Phaseolus, Ricinus, Zea, Primula, Impatiens, Pelargonium, Triticum, 

 and Helianthus. He found no constant relation between the number and 

 size of stomata in relation to unit area of leaf surface and the amount of trans- 

 piration. He also concludes that the amount of transpiration is not governed 

 entirely by stomatal regulation. His work, however, does not show any 

 explanation for any other control. 



In one of the most recent publications upon this subject, by Bakke and 

 Livingston, 21 data are given upon the daily march of foliar transpiring power of 

 different leaves of plants of Xanthium and Helianthus. These serve to empha- 

 size the fact that the control of foliar transpiration by the plant is a complex 

 one, especially as there is a great range in transpiring power among the differ- 

 ent leaves of the same plant with considerable variation in time of the diurnal 

 maxima. No very definite relation is established between age of leaves and 

 their behavior, except that the oldest ones always show a low daily range of 



18 Briggs, L. J., and Shaxtz, H. L., Hourly transpiration rate on clear days as 

 determined by cyclic environmental factors. Jour. Agric. Research 5:583-649. 1916. 



19 j ,\ n automatic transpiration scale of large capacity for use with freely 



exposed plants. Jour. Agric. Research 5:117-132. 1915. 



Muenscher, W. L. C, A study of the relation of transpiration to the size and 

 number of stomata. Amer. Jour. Bot. 2:449-467. 1915. 



21 Bakke, A. L., and Livingston, B. E., Further studies on foliar transpiring 

 power in plants. Physiol. Researches 2:51-71. 1916. 









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