524 EXPERIMENT STATION RECOED. 



The causes of transpiration and of retention of water vapor by plants, 

 Leclkkc du Sablon {Rev. G6n. Bot., 25 {1913), Nos. 290. pp. .'i9-83 : 291, pp. 

 104-124; abs. in Zcntbl. Zool. Allg. u. Expt. Biol., 3 {1913), No. 5, pp. 175, 176). — 

 In continuance of previous work (E. S. R., 26, p. 430), the author studied trans- 

 piration as sliown by different plants subjected to various factors and conditions. 



As a result he states that in general those circumstances which tend to con- 

 tract the protoplasm diminish the permeability of the membrane and may 

 thereby enormously reduce transpiration, other factors remaining the same. 

 Plasmolysis may reduce transpiration considerably. Anesthetics first diminish 

 transpiration, apparently by contracting the protoplasmic cell membrane; after 

 a period of resistance a pathologic condition seems to ensue, the protoplasm 

 relaxing, when transpiration may greatly increase. This increase may con- 

 tinue so long as the plant lives. In variegated or in colorless plants, both direct 

 and diffused light heighten transpiration in somewhat the same degrees as in 

 green plants, no exclusive part being played apparently by chlorophyll in the 

 absorption of solar energy; and the same general statement applies in the case 

 of heat, which also heightens transpiration. Fleshy succulent plants or parts 

 show low transpiration rates, corresponding to the low permeability of their 

 protoplasmic membranes and their slight sensibility to heat and light, these 

 characters being marked in case of plants habituated to dry conditions. 



The author concludes that elevation of temperature augments transpiration 

 through increase of vapor tension in a purely physical way and independently 

 of other causes, also through increase of permeability, this effect being physio- 

 logic-al and depending upon the characters of the plant itself; also that solar 

 energy influences transpiration directly by affecting the permeability of the cell 

 membranes, this being also physiological and variable according to the plant 

 tissues involved, as well as indirectly by elevating the temperature, no direct 

 and necessary relation of chlorophyll as such to transpiration being inferred, 

 but the general parallelism between the two being ascribed to the structure 

 necessary to gaseous exchange, which it is held inevitably entails some corre- 

 spondence as regards transpiration ; and finally that while evaporation at the 

 surface of the cell is a physical phenomenon involving risk to the plant, the 

 retention of water is a physiological fimction indispensable to life. 



A brief bibliography is appended. 



The ascent and descent of water in trees, A. J. Ewakt {Proc. Roy. Sac. 

 Victoria, n. ser., 25 {1912), No. 1, pp. 115-119, pi. 1). — Continuing former in- 

 vestigations (E. S. R., 23, p. 26). regarding the part played by living cells in 

 sap ascent, the author experimented with a 4-year-old tree of Acacia inollissimu 

 25 ft. high and 26 in. in circumference near the ground where, after surround- 

 ing the trunk with water, both bark and wood were cut cleanly away to a 

 depth of 1* in. Copper sulphate was then added to make up a 5 per cent solu- 

 tion in contact with the cut surface. 



The rate of absorption, at first rapid, later began to fall off considerably. 

 After 26 liters had been absorbed in 4i hours eosin was substituted. Its absorp- 

 tion was much slower and in turn showed a decrease. It was later found that 

 the eosin was largely fixed in the walls of the wood vessels with very little 

 lateral diffusion, showing the almost exclusive part played by the wood vessels 

 in the ascent of the sap. The eosin was held back to such an extent as to render 

 it useless as a measure of the sap movement ; for when the tree was cut down at 

 the end of the third day the red dye had risen only about 10 ft., being restricted 

 to the outer layers of wood from 1 to 1.5 in. in depth at the base, thinning 

 out upward to 0.25 in. Traces of copper were detected in the outer wood at 

 the top of the tree. At the same time it was found that the eosin had traveled 

 down the stem, showing as far as 7 ft. along the lateral roots to those 0.5 



