PLANT PHYSIOLOGY 201 



P. brachypus the number varies from 3 to 4, whilst 4 is normal 

 for P. ovatum. Similarly, with respect to the stamens in two 

 species, there are normally 6 stamens, in others there are 5, 

 in still others the number varies from 5 to 6, whilst in 

 P. Heeriammi there are 3-6 stamens and in P. ovatum 4. The 

 latter is the only species with pinnately veined leaves. 



PLANT PHYSIOLOGY. By Prof. J. H. Priestley, D.S.O., B.Sc, 

 F.L.S., Botanical Department, University of Leeds, (Plant Physiology 

 Committee.) 



Some Recent Work on Proteins in its Relation to Physiology. — 

 One of the difficulties of the plant physiologist, and of the 

 botanist who would follow the development of plant physiology, 

 is the constant demand made upon him to assimilate and utilise 

 the knowledge and technique developed in widely different 

 fields of investigation. 



As the writer thinks that a recent series of papers by Jacques 

 Loeb are of the utmost importance in plant physiology, an 

 attempt is made in the following pages, not to summarise the 

 work, but to indicate by an elementary discussion the nature 

 of the conclusions reached by Loeb. The papers themselves 

 are cited at the end of this review, and references are also given 

 to two valuable summaries of this work published by Loeb 

 himself. 



Loeb's work deals with the relation of proteins to electrolytes, 

 and the key-note to the new standpoint is to be found in the 

 attention paid to the effect of the hydrogen ion concentration 

 upon the behaviour of the proteins. 



This conception itself awaits application in almost every 

 field of physiological investigation, and as it is not yet familiar 

 to many botanists, it deserves further consideration. 



It has long been realised that the acidity or alkalinity of the 

 watery medium in which the reactions of the protoplast proceed 

 is a factor of great physiological importance. The closer in- 

 vestigation of this question required a quantitative estimation 

 of the sap reactions. The usual measure of acidity utilised by 

 the physiologist has been the amount of standard alkali required 

 to render the acid solution neutral, as indicated by the colour 

 change of an indicator. The exact amount of alkali needed 

 has therefore depended, to some extent, upon the indicator used, 

 as different indicators would change colour upon the addition 

 of different amounts of alkali. 



Equivalent quantities of a "weak" organic or "strong" 

 mineral acid give the same titration value for acidity if 

 measured in this manner, although, as the common use just 

 made of the terms " weak " and " strong " imphes, there are 

 real differences, not in the equivalence of the quantities of acid 



