RECENT ADVANCES IN SCIENCE 563 



mechanical theory of ascent of sap, and Nordhausen is driven 

 back to the " living cell " explanation of water conduction, 

 inadequate and unsatisfactory as this position is. 



Farmer (Proc. Roy. Soc. 90, B, 218-31, 232-50, 191 8) 

 has measured the conducting properties of the wood of a 

 variety of stems, finding that evergreens exhibit a relatively 

 low conductivity compared with that of deciduous species, 

 whilst the latter show more readiness to react to environment. 

 The suggestion is made that wood structure rather than habitat 

 is correlated with xerophytism. 



Confirmation is being obtained from many sources of the 

 presence of a regulating factor in plants which retards transpira- 

 tion towards noon and decreases the transpiring power whilst 

 atmospheric conditions are still tending to increase the rate of 

 water loss. Livingston (Cam. Inst. Publ. No. 50, 1906, and Bot. 

 Gaz. 53, 309, 1 91 2) first established the existence of the pheno- 

 menon, and attributed it to the lowering of leaf water content. 

 The results have been confirmed by several workers using 

 various methods, including the hygrometric paper test, which 

 has now been thoroughly standardised and tested and may be 

 regarded as satisfactory. See Shreve (Cam. Inst. Publ. No. 194, 

 1914), Trelease and Livingston (Journ. Ecol. 4, 1, 1916). Bakke 

 and Livingston (Physiological Researches, 12, 1916) and Knight 

 (Ann. of Bot. 31, 221-40, 191 7). 



Progress has been made in the study of atmometry, first 

 adapted to transpiration work by Livingston (Plant World, 18, 

 21, 51, 95 and 143, 191 5). Recognition of the complexity of 

 the climatic factors influencing water loss by the plant has 

 led to considerable development of the methods of control. 

 Johnston and Livingston (Plant World, 19, 136-40, 191 6) have 

 used a convenient atmometer adaption which permits the 

 frequent measurement of evaporation rate over periods of a 

 few seconds. Blackman and Knight (Ann. of Bot. 31, 217, 

 191 7) have devised an " air flue " for the control of air move- 

 ment in transpiration experiments, and this has also been used 

 with advantage. 



Other aspects of the climatic factor have been presented in 

 various papers. Ihomas and Ferguson (A nn. of Bot. 31, 241-55, 

 191 7) discuss the calibration of atmometers by comparison 

 with water surfaces, and show by experiment that the method 

 is not justifiable except under very particular conditions. 



