568 DR. A. J. EWART ON ASSIMILATORY INHIBITION. 
also die in a longer but also relatively very short time. Vochting 
concludes that the leaves lose the power of assimilation—an 
assumption which is not justifiable without direct experimental 
evidence for the same being given, and which leaves the questions 
as to whether the loss of the power of assimilation precedes or is 
concomitant with death, and whether, if the former be the case, 
recovery is possible, unanswered. 
Mimosa does not form very favourable material for experi- 
mentation in this direction, as the leaves are very sensitive and 
are very readily fatally injured, but with potatoes very good 
results were obtained. 
Direct observation shows that the leaves formed on the etiolated 
shoots of potatoes grown in darkness are yellowish, very small, 
and show no power of assimilation. Exceptionally leaves nearly 
2 em. long with a terminal leaflet 0:5 to 0'8 cm. long may be 
found, but generally the leaves are very much smaller than this. 
If such etiolated shoots are exposed to light in an atmosphere 
kept free from CO,, the leaves grow slightly and turn green, but 
soon become bluish green and do not become longer than 1 cm. 
in length, then turning yellow and slowly dying. The chloro- 
phyll grains of leaves which have turned green under these 
conditions are normal in shape and deep green or bluish green 
in eolour, but the leaves show only a weak power of assimilation, 
which in a few cases is in parts fairly active. The power of 
assimilation often varies in different parts of the same leaf, 
being in parts weak and in parts imperceptible. Many quite 
green leaves of various sizes (08, 0'4, 0-5, and 0:8 em. long) 
show no perceptible power of assimilation. A portion of the 
leaf is examined and the rest left attached, the cut surface being 
covered with vaseline. Such leaves, on the plant being exposed 
to normal CO, containing air, frequently die, but may recover, 
resume growth, and finally show active assimilation. It is prob- 
ably often the injury which causes the death of the leaf and 
prevents recovery. Leaves with even a slight yellowish tinge 
show no power of assimilation or recovery. 
The stem also turns green. In the younger parts of the stem 
the outer cortex has well-defined fairly dark-green chlorophyll 
grains, but has no power of assimilation. In the inner cortex a 
faint power of assimilation may be present. In the central 
parenchyma the colour is much fainter, the chlorophyll grains are 
less well defined and in some cases almost undifferentiated; but 
