208 SECTIONAL ADDRESSES. 
the conceptions of cecology correlated a mass of isolated facts and made 
possible a logical presentation of the subject within twenty-three years of 
the publication of Grisebach’s ‘ Vegetation of the Earth in relation to 
Climate’; Warming’s (cology of Plants first appeared in 1895, and 
Schimper’s Plant Geography followed three years later. 
The direct and great value of the cecological study of plants has been 
the recall of botanists to the field and sending them back from whence 
they came with fresh problems for investigation; in addition, it has 
stimulated the study of taxonomy, causal morphology, and physiology. 
Laboratory work was one of the reasons for the decline, at any rate, in 
this country, of the study of taxonomy in that it attracted men who 
otherwise might have been pure systematists. In physiology much recent 
work is a direct outcome of cecology, the considerable investigations on 
the water economy of the plant is but one example. 
Physiology. At the beginning of this period the problem of the ascent 
of sap was still moot. Sachs persisted in his imbibition theory, notwith- 
standing the many facts ranged against it. Strasburger’s experiments 
pushed home the idea that the phenomenon was entirely physical, a view 
which was adopted by Askenasy, and Dixon and Joly (1895) who realised 
the significance of the tensile strength of water and on it founded their 
well-known explanation. Concurrently, the splendid lead given by Pfeffer 
and de Vries was vigorously followed and the problems of permeability, 
osmotic pressure, and, in general, the water relations of the cell were 
the subject of hundreds of papers. Amongst the scores of workers 
engaged, these were prominent: 8. C. Brooks, G. Clowes, Czapek, Dixon 
and Atkins, Girard, Lepeschkin, Loeb, Osterhout, Ostwald, Ruhland, 
Stiles, Ursprung and Blum, and MacDougal. 
It is impossible here to attempt a survey of the progress of this wide 
and difficult branch of physiology. The mechanism of permeability and 
the physico-chemical problems involved are still matters for discussion, 
but, on the other hand, the considerable forces available in osmotic 
pressure, the plasticity of the living cell in the adjustment of its osmotic 
machinery and the nature and importance of turgidity have given us a 
reasonably clear understanding of the uptake of water and its movements 
in the tissues. 
Mention also must be made of the progress of knowledge of the gaseous 
diffusion into and out from the ordinary leaf. This had been a matter of 
dispute and some thought that the main path was through the intact 
walls of the leaf epidermis (cuticular diffusion) rather than through the 
stomates. The varying experimental results obtained by different workers 
were due, in the main, to faulty technique. Stahl (1894) demonstrated 
that if the stomates are effectively blocked, no carbon assimilation will 
take place. His results were confirmed by F. F. Blackman, who at this 
time (1895) was beginning his well-known investigations on carbon 
assimilation and respiration. Blackman showed that the evolution of 
carbon dioxide during respiration and its intake during carbon assimilation 
was, in general, proportional to the number of stomates on the leaf 
surfaces. These results were confirmed by Brown and Escombe (1905) 
who had been investigating the subject for some years. Their classic 
work on the static diffusion of gases was published in 1900, the kernel of 
