714 Thoday. — On the Effect of Chloroform on 
disorganization, the rate of absorption of oxygen was, on the contrary, 
greatly depressed. This change of colour is attributed to the oxidation of 
substances of the nature of tannins, 1 present in the Laurels and Helianthus , 
but not in Tropaeolum , owing to the activity of oxidases which follows as 
a result of the fatal influence of the chloroform. As is already well known, 
the breaking down of the organization of the leaf-cells of the Cherry Laurel 
is also followed by the production of hydrocyanic acid, owing to the 
hydrolysis of the cyanogenetic glucoside prulaurasin by an emulsin. 2 
The other fact of general importance is that during the temporary 
augmentation, or stimulation, of the respiration which follows less drastic 
treatment in all the leaves studied, the absorption of oxygen and production 
of C0 2 apparently still remain co-ordinated. The ratio between the quantities 
of oxygen and C0 2 concurrently absorbed and evolved shows indeed small 
changes; but such changes were not always observed, and they appear to 
differ in different kinds of leaves, though within the same kind some degree 
of concordance is shown. 
A very interesting point is suggested by the character of the stimulation 
curves obtained in most of those experiments in which the leaves had pre- 
viously been starved in the dark. These curves indicate a relatively greater 
and much more prolonged augmentation of the respiration, in comparison 
with the low rate of respiration characteristic of their starved condition. 
The same effect was not, however, obtained in all the experiments, and 
further investigation is necessary before a discussion of its significance and 
the conditions on which it depends would be profitable. 
The transition from stimulation, with the production of C0 2 and 
absorption of oxygen still closely correlated, to disorganization and the 
complete breakdown of this correlation would appear to be sharply marked ; 
for not only is the difference between doses which merely stimulate and 
doses which initiate disorganization very small, but intermediate doses may 
initiate disorganization in one part of a leaf and not in another, this part 
remaining green for a long time. It is interesting that even in leaves of 
Cherry Laurel disorganization only slowly spreads to parts which have been 
left green, notwithstanding the evolution of prussic acid from the disorganized 
areas. 3 
1 In the case of Aucuba , the blackening of the leaves is said to be independent of oxygen. See 
Maquenne and Demoussy, Comptes rend., cxlix, 1909, p. 957. 
2 According to Weevers (loc. cit., p. 254) the HCN is detected, even by its odour, later than the 
beginning of the brown coloration, as it has first to diffuse out of the leaf. 
3 Weevers has found that the darkening of leaves may only begin some time after exposure to 
chloroform. He supposes (loc. cit., p. 261) that where this happens death has already taken place 
during exposure. The other alternative would appear, however, to be conceivable : even if, as Weevers 
holds, necrobiosis and stimulation be sharply distinct from each other, necrobiosis might still be 
preceded by stimulation and, in cases of deferred coloration, set in after exposure, not as a direct 
effect of the chloroform but through excessive stimulation of the normal respiratory processes. 
Prolonged starvation alone leads eventually to increase of permeability and necrobiosis. 
