DB. A. J. EWART ON ASSIMILATORY INHIBITION. 557 
Cotyledons slightly paler, chlorophyll grains slightly smaller and almost 
unchanged, but no evolution of O. Plants with one cotyledon used for 
sections brought into light, the other cotyledons mostly after 2-3 days 
begin to turn green and show whilst still yellow (2nd day) a faint evolu- 
tion of O, stronger on the 3rd day. 
Phaseolus multiflorus.—Primary simple leaves, lamina 25 by 1:5 cm., and 
quite deep yellow, show a quite distinct but only weak evolution of O. 
The younger trifoliate leaves are from pale yellow to almost colourless, 
and show no perceptible evolution of Ó. In older plants the primary 
leaves are slightly paler, and assimilation is now absent or almost imper- 
ceptible. If the plant is now brought into light such leaves in some cases 
may recover, become green, and commence to assimilate, but in most cases 
slowly die. 
It appears, therefore, that etiolated chlorophyll grains developed 
in perfect darkness may possess a weak power of assimilation. 
The preparations are made in weak light, at once placed in 
darkness until the Bacteria come to rest, then exposed to light 
and examined, the total exposure previous to examination 
being never more than a few minutes. Sections in closed cell 
preparations do not turn perceptibly green when exposed to 
light, however long they may remain living. To make absolutely 
certain that the evolution of oxygen was not perhaps due to the 
formation of traces of chlorophyll during the necessary few 
minutes’ exposure, test preparations from adult etiolated cotyle- 
dons grown in perfect and continuous darkness were made in a 
photographic dark room in weak red lamp light and then at once 
examined as usual, when the same power of assimilation was 
shown as before. 
Another possibility was that the etiolated cotyledons had 
perhaps the power of forming traces of chlorophyll, though not 
sufficient to make them perceptibly green, thereby being capable 
of showing weak assimilation. 
Thus in a few of the Helianthus seedlings, though grown from 
the first in perfect darkness, the cotyledons are partially or 
almost entirely dark greenish on the outer surface. Micro- 
scopical examination of transverse sections shows that the 
chlorophyll grains of the outer epidermal layer, and in a few 
cases of the mesophyll layers immediately beneath, have a distinct 
greenish tinge. Living sections of such cotyledons examined 
by the Bacterium method show a stronger evolution of oxygen 
from the inner palisade parenchyma layer, which is always quite 
yellow, than from the outer spongy mesophyll layer, even though 
