127 
R. C. Knight. 
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RECENT WORK ON TRANSPIRATION. 
By R. C. Knight, D.Sc. 1 
[Department of Plant Physiology and Pathology, Imperial 
College of Science and Technology ). 
R ESEARCHES on transpiration in recent years have resulted 
in the recognition of the complexity of the system involved 
in the regulation of the rate of water-loss from a plant. It has 
been realised that the control of water-loss is not a simple process, 
dependent mainly on stomatal change, but that its regulation is 
shared by a number of widely different factors, which are never¬ 
theless more or less closely interrelated. Some of these 
regulating factors may be described as external, pertaining to 
atmospheric and climatic conditions, such as temperature, atmo¬ 
spheric humidity, and light; whilst others are classed as internal, 
that is, pertaining to the structure and condition of the plant. 
Examples of the latter are stomatal aperture and the supply of 
water to the transpiring leaf cells. 
Transpiration being essentially a process of evaporation, 
external factors may be expected to influence the process in much 
1 Dr. Knight’s paper forms a useful summary of work on the current 
problems connected with transpiration which are being attacked by plant 
physiologists. It contains some account of the author’s own unfinished 
researches, including the methods he has adopted and some partial results. 
Under ordinary circumstances it wonld have been undesirable to publish 
these, but in view of the temporary removal of the author from research 
owing to the national crisis it has seemed legitimate to include them. 
[Editok N.P.] 
