200 SECTIONAL ADDRESSES. 
of the animal cell, and his views were supported by the observations of 
de Bary on the mycetozoa. 
With the passing of time it was recognised that the protoplasm of the 
plant and of the animal is identical and that it is the basis of life, a 
conclusion to which Payen, Cohn and Max Schulze contributed much. 
Towards the end of this period, the improvement of microscopical 
technique led to great discoveries in the details of nuclear division. In 
this the work of Strasburger is outstanding, and to him is due the main 
eredit of firmly establishing that aspect of botany now called cytology. 
The contributions of Fleming and of Schmitz must, however, not be 
overlooked, nor those of Guignard who, unfortunately, prejudiced his 
own work by his description of structures which had no existence. 
Physiology—Our knowledge of osmotic phenomena is founded on 
Dutrochet’s (1827) studies on differential diffusion through a colloidal 
membrane. Graham, the father of colloid chemistry, showed (1854) that 
the rate of this diffusion depended, inter alia, on the nature of the membrane. 
This led to Traube’s discovery of the co-called artificial cell produced by 
dropping a crystal of copper acetate into a solution of potassium ferro- 
cyanide, whereby a precipitation membrane of copper ferrocyanide 
surrounding the copper acetate is produced ; the reacting salts thus become 
separated by a semi-permeable membrane and the ‘cell’ grows. This 
observation, which is periodically rediscovered, was used by Pfeffer (1877) 
who supported the membrane of copper ferrocyanide in the wall of a 
porous pot and with it made many highly important observations, more 
especially the facts that the osmotic pressure is proportional to the 
absolute temperature and to the concentration of the solution. Thus 
was born a branch of physical chemistry and one of the first results was 
van ’t Hoff’s theory of solutions. At this time de Vries also was busy 
on the problem and contributed much ; to students he is best known by 
his plasmolytic method by means of which he ascertained the isotonic 
co-efficients of many substances. 
The mention of osmotic phenomena naturally leads to the ascent of 
sap and transpiration. Hales was the pioneer and his work is classical ; 
many years later (1837) he was followed by Dutrochet, who was the first 
to distinguish betweem root-pressure and the pull of transpiration. Later, 
the solution of the problem was essayed by Unger, Boehm, Sachs, Elfving, 
Hartig, von Héhnel and many others: the questions whether the water 
travelled as water of imbibition or through the lumina of the trachee 
and whether the rise was entirely a physical phenomenon or was dependent 
on the vitality of the parenchyma of the wood, were warmly discussed. 
Those interested in the history of the subject will find a good account in 
an unlikely place, in Marshall Ward’s ‘ Timber and some of its Diseases ° 
(London 1897). 
Hales, Priestley, Senebier, Ingen Housz and de Saussure were the 
pioneers in the study of carbon assimilation, with the result that the more 
obvious facts were known before 1831. Of these men, de Saussure was 
the greatest: he was the first to strike a balance sheet which indicated 
the unity of the photosynthetic quotient, a fact confirmed by Boussingault 
in 1864, and he was the first to show that water and salts, as well as carbon 
dioxide, were essential for the nutrition of the green plant. His work, 
Die ott ae Pete. Ce ee ee) 
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