364 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
On Assimilatory Inhibitionin Plants. By ALFRED JAMES EWART, 
B.Sc. (Lond.); 1851 Exhibition Scholar; late Demonstrator 
of Botany in University College, Liverpool. (Communicated 
by R. J. Harvey Gissox, M.A., F.L.S.) 
[Read 21st November, 1895.] 
ASSIMILATION, like any other plant function, is liable to be 
modified by the external conditions under which a plant may 
happen to be. Thus as regards temperature, there is a minimal, 
optimal, and maximal point for assimilation, just as there is for 
respiration, though the optimal, minimal, and maximal points 
for the two functions do not necessarily coincide. Assimilation 
may, however, also be modified by internal conditions, about 
which very little is known. Thus Dehnecke* came to the 
conclusion, mainly from theoretieal deductions, that green, 
non-assimilating chlorophyll bodies having the function of a 
leucoplastid, and not of a true chlorophyll body, are of common 
occurrence in green plants. Similarly Jumelle + found that as 
the result of subjecting lichens and mosses to dry heat, a con- 
dition might be induced in them during which they had lost the 
power of assimilation, but still continued to respire. Further 
research in this direction being evidently necessary, I undertook, 
at the suggestion of Prof. Pfeffer, a series of investigations to 
determine the various causes by which this condition of what 
we may term assimilatory inhibition may be produced and the 
phenomena connected with it. 
lt was at once evident that the method used by Jumelle was 
not so well adapted for a research of this kind as is a microscopical 
method, allowing more rapid observations and more detailed 
examination of the cells or tissues affected to be made. There 
are three well established methods by which a microscopical 
determination of the evolution of Oxygen by green assimilating 
cells in the presence of light can be made. The first and most 
important of these is Engelmann's f well-known Bacterium 
* Dehnecke, “ Ueber nicht assimilirende Chlorophyllkérper.” Inaugural- 
Dissertation, Universitat in Bonn (Cóln, 1880). 
t Jumelle, “ Recherches Physiologiques sur les Lichens," in Revue Générale 
de Botanique, vol. iv. 1892, pp. 114, 159, 220, & 259. 
t T. W. Engelmann, “Neue Methode zur Untersuchung der Sauerstoff- 
ausscheidung pflanzlicher und thierischer Organismen," in Bot. Zeit. Bd. xxxix. 
(1881) No. 28, 
