RECENT ADVANCES IN SCIENCE 123 



BOTANY. By F. Cavers, D.Sc, A.R.C.Sc. 



Plant Physiology. — That despite the large amount of work done 

 on the transpiration of plants we are still very much in the 

 dark regarding this important process is emphasised by 

 Muenscher (Amer. Jonrn. Bot. 2), whose results are not the 

 less valuable because negative. He finds no constant relation 

 to hold between the amount of water lost and ( 1 ) the numbers 

 of linear units of stomatal pore, i.e. number of stomata per unit 

 of leaf surface multiplied by length of average pore, or (2) the 

 length of the pore of one stoma, or (3) the number of stomata 

 per unit of leaf surface. These results, based on the study of 

 a fair range of species, should clear the way for further work, 

 since they show that the variations in amount of transpiration 

 in different plants cannot be accounted for by size and number 

 of stomata, but must be explained by a complex of several 

 factors. Trelease and Livingston (Journ. Ecol. 4) give the 

 results of a detailed study of the daily march of transpiration 

 as indicated by the porometer and by standardised cobalt 

 paper, and show that although the graphs obtained by the two 

 methods appear to disagree, they are found on closer analysis 

 to afford, taken together, extremely valuable indications of 

 transpiring power in plants. In an elaborate paper Briggs and 

 Shantz {Journ. Agric. Res. 5) discuss the hourly transpiration 

 rate on clear days as determined by cyclic environmental factors, 

 after giving data of simultaneous automatic records of solar 

 radiation intensity, depression of wet-bulb thermometer, air 

 temperature, wind velocity, evaporation from a free-water sur- 

 face, and rate of water -loss of various plants. Least-square 

 reductions of the dependence of transpiration upon radiation 

 and air temperature, or upon radiation and saturation deficit, 

 do not account entirely for the observed transpiration, though 

 a satisfactory agreement between computed and observed evap- 

 oration is obtained by the use of these environmental factors; 

 that is, the plant undergoes changes during the day which 

 modify its transpiration coefficient. These results support the 

 conclusion of other recent workers that plants under conditions 

 favouring high transpiration do not respond wholly as free 

 evaporating systems, even if abundantly supplied with water 

 and suffering no visible wilting. 



The interesting problems centred around the permeability of 

 cells to different ions have been worked at by various botanists 



