K.— BOTANY 215 



of respiration and salt and water relations that I propose mainly to deal 

 in this address. 



Inasmuch as investigations into these various aspects of vital activity 

 involve different techniques, it is not surprising that our knowledge of 

 them has developed to a large extent independently. They are, of course, 

 not independent, for it must be realised that the functioning of the plant 

 machine depends on the harmonious working together of all plant pro- 

 cesses. And that the various aspects of our subject mentioned above are 

 closely connected is now, for the most part, fairly clear. It is obvious 

 that, since all vital activity depends on the presence of protoplasm, the 

 chemical and physical constitution of that substance must determine that 

 activity, while, coming to details, many investigators have sought to connect 

 the passage into and out from the cell of water, and particularly of dissolved 

 substances, with the existence of limiting plasmatic layers of a constitu- 

 tion different from the inner part of the protoplasm. The composition 

 of the vacuole determines without doubt to a very great extent the absorp- 

 tion of water by the vacuolated cell. This absorption is, however, also 

 dependent on the presence of protoplasm, since when this is destroyed, 

 the water relations of the cell are quite altered. Enzymes are only pro- 

 duced by living tissues and their production presumably depends on the 

 presence of protoplasm. Respiration, again, is a function of living cells, 

 and, although exact proof may still be wanting, it is almost certain that 

 enzymes are intimately concerned in the respiratory process. That the 

 solute relations of cells are intimately connected with respiration is not so 

 obvious, but that this is probably the case I indicated first in 1927, and later 

 work has left this connection in little doubt, although the nature of the 

 connection is not so evident. 



With regard to the protoplasm itself, it is now generally recognised that 

 it forms a colloidal system of probably a number of phases in which the 

 chemical constituents have as their basis water, proteins and complex 

 fatty substances. Carbohydrates are also constantly present in protoplasm, 

 but whether they are to be regarded as dead inclusions playing no essential 

 part in vital behaviour, or whether they are necessary for the maintenance 

 of protoplasm in its living condition, is not clear. Nor is it at all clear 

 how these various substances are distributed among the various phases. 

 It is sufficient indication of the doubt that surrounds the problem of the 

 constitution of protoplasm that one authority on it emphasises its generally 

 low viscosity, while another lays stress on its slimy character. One regards 

 it as having the character of a suspensoid, another that of an emulsoid. 

 If we accept the reports of observations on the physical qualities of 

 protoplasm, and there is no reason for supposing that the majority of such 

 observations are incorrect, we must inevitably conclude that protoplasm 

 varies very considerably in its constitution from one object to another, 

 and probably in the same material at different times. In general, how- 

 ever, there is little difference to be observed under the microscope, or 

 even the ultramicroscope, between samples of protoplasm from widely 

 different materials, yet there must be fundamental differences between 

 the protoplasm of different species. What these differences are, whether 

 they are subtle chemical differences or differences in arrangement of 

 molecules or molecular aggregates, is a matter on which our ignorance 



