MR. A, J. EWART ON ASSIMILATORY INHIBITION. 871 
CO, that they can assimilate in the same time under optimal 
illumination. Hence the possibility of error introduced by using 
the evolution or non-evolution of oxygen asa test for the presence 
or absence of assimilation is at ordinary temperatures but slight. 
Practically, whenever a cell examined by the Bacterium method 
under optimal illumination shows no evolution of oxygen, the 
power of assimilation is absent. At high temperatures, how- 
ever, since respiration, according to Kreusler *, and Bonnier and 
Mangin t, goes on continually and more and more rapidly, in- 
creasing with each rise of temperature, whilst according to 
Kreusler the assimilatory curve sinks, the possibility of a power of 
assimilation being present, though no evolution of oxygen can 
be detected, is much increased. In the following pages all the 
observations were, with a few exceptions on pp. 386, 387, made 
at a temperature not above 20? C. In any case, what is certain 
is that where no evolution of oxygen is taking place, no increase 
of plastic material can occur, though the waste of substance by 
respiration may be partially compensated for by weak assimi- 
lation. In actual experimentation it has been found that an 
assimilation and evolution of oxygen, which are imperceptible by 
the gas analytical method, can be readily detected by the more 
delicate and discriminatory Bacterium method. 
When a preparation is made of a living leaf in which assimi- 
lation has been temporarily inhibited, in almost all cases the 
Baeteria come to rest sooner in the neighbourhood of the leaf 
than out in the open field. This is because the leaf, though it 
no longer assimilates, still respires, and the oxygen dissolved in 
the enclosed water is sooner exhausted in its immediate neigh- 
bourhood than it is further away. That such stoppage is not 
due to the extrusion of mucilage or other substance, exercising 
a retarding influence upon the movement of the Bacteria, by the 
leaf, is shown by the fact that the Bacteria move longer in the 
neighbourhood of a freshly-killed leaf than they do out in the 
open field. 
A normal moss-leaf may remain living and assimilating, in 
water in a closed chamber with Bacteria, exposed to diffuse day- 
light for weeks. When, however, assimilation has been tempo- 
rarily inhibited, the return is slower in a mounted leaf than in 
* Kreusler, “ Beobachtungen über die Kohlensaure-Aufnahme und -Ausgabe 
der Pflanzen,” in Landw. Jahrb. 1887, Bd. xvi. pp. 711-715. 
T Bonnier and Mangin, in Aun. d. Sc. Nat. 7 sér. ii. 1885, p. 378, 
