ai4 SECTIONAL ADDRESSES 



plant are related to the protoplasm, but although the cellular structure of 

 plants had been recognised with the work of Hooke, Grew and Malpighi 

 in the seventeenth century, the discovery of protoplasm and appreciation 

 of the supreme importance of this substance only dates from 1835, when 

 Dujardin described the protoplasm, or sarcode, as he called it, of animal 

 cells. The importance of protoplasm in the plant appears not to have been 

 recognised until 1846. The credit for this is due to von Mohl, although he 

 cannot, as Sachs asserted, be credited either with the discovery of proto- 

 plasm or with the invention of its name. 



In spite of the fact that by the end of the first half of the nineteenth 

 century the connection between protoplasm and life must have been 

 evident, little attempt was made for many years towards a serious investiga- 

 tion of the properties of this substance, or to determine the general 

 activities of the protoplasm as manifested by every living cell. This may 

 have been due partly to the traditional outlook on plant physiology, which 

 had emphasised the nutritional relationships, and partly to the impetus 

 given to other aspects of botany by Hofmeister's work on the life history 

 of plants and by the publication of the Origin of Species, which diverted 

 thought on botanical matters to problems of descent and comparative 

 morphology. And yet even as far back as 1828 Turpin had put forward 

 the idea that the cell is the elementary primary organism, and the plant 

 built of these cells a sort of community or colony of such elementary 

 organisms. This view appears to have enjoyed considerable popularity 

 for a time. It is found in Meyen's Neues System der Pflanzenphysiologie 

 published in Berlin in 1837, ^"d was held in no uncertain fashion by as 

 distinguished a botanist as Schleiden, and even appears as late as 1861 

 in the fourth edition of his Grundziige der wissenschaftlichen Botanik, 

 although it should be pointed out that this was no more than an unaltered 

 reprint of the third edition of 1849. Such a view is, of course, as wrong 

 as one which takes no account of individual cell activities. Phenomena 

 of nutrition, development and irritability combine to refute such an idea. 



There are, nevertheless, activities which are characteristic of all living 

 cells. They all exhibit respiration in the sense of a release of energy from 

 substances present in the cell, a release which in the very great majority 

 of plants is brought about by the oxidation of carbohydrate or fat. Again, 

 all living cells are capable of absorbing water and dissolved substances, 

 and of giving out these materials under certain conditions. For an under- 

 standing of these activities a knowledge of the system in which they take 

 place is important, so that the study of the cell system, and in particular 

 of the protoplasm, comes within the sphere of inquiry of the general cell 

 physiologist. This includes the study of enzymes, which undoubtedly 

 plays an extremely large part in protoplasmic activity. 



Thus investigations in general cell physiology fall for the most part into 

 four groups, namely (i) those concerned with the chemical and physical 

 constitution of the protoplasm and other cell constituents ; (2) the study 

 of enzyme action ; (3) those dealing with absorption and excretion of 

 water and dissolved substances which have, for the sake of convenience", 

 generally in the past been referred to as problems of cell permeability ; 

 and (4) those concerned with respiration. The first two are largely 

 biochemical studies, and it is with the more purely physiological problems 



