572 DR. A. J. EWART ON ASSIMILATORY INHIBITION. 
Helianthus annuus.—Young seedlings with etiolated cotyledons in CO,-free 
air turn in 1 day quite green (as rapidly as in normal air), and show 
quite active assimilation. (a) After 7 days—plant, cotyledons 2 by 1-2cm., 
quite green, and shows rather weak but distinct evolution of O. (6) After 
11 days—plant,'cotyledons 2-5 by 1 cm., faint yellowish tinge, no evo- 
lution of Ó ; 1st pair of leaves 1:5 by 7 cm., yellowish, and no evolution 
of O. In air the tips of these leaves and tip of cotyledon die; rest remain 
living, recover, and show active assimilation. (c) Cotyledons 2 by 1:2 cm., 
lst leaves 06 by 03 cm., yellowish tinge almost imperceptible. No 
evolution of O or (d) faint trace of assimilation in parts ‘cf cotyledons, 
none in Ist leaf. In air both (c) and (d) recover and resume growth. 
Etiolated seedlings of the same age kept for the same time in darkness 
almost all turn green, and remain living when brought into light. 
Cucurbita Pepo.-—Seedlings. In 1 day the cotyledons are quite green and 
show an active evolution of O. (a) After 5 days cotyledons 6 by 2:5 cm., 
and still green, show weak to moderately active evolution of O. Ist young 
leaf (lamina 1:3 by 1 cm.) green, but: apex yellowish ; taint evolution of O 
at base only. Sucha plant in air recovers entirely, and shows in 2-3 days 
active assimilation in cotyledons and Ist leaf. (b) After 10 days, coty- 
ledons in parts slightly brownish or yellowish green; no evolution of O. 
In air plants recover, and in 2-3 days show active assimilation. 
(c) After 13 days, cotyledons yellowish over greater part. No evolution 
of O. In 2 days in air part of 1 cotyledon remains green and shows weak 
assimilation, but in 3-4 days entire plant dies. Similar plants kept in 
darkness for the same time nearly all turn green and remain living in light. 
Etiolated seedlings, therefore, in darkness remain living for a 
longer time than if exposed to light, but are prevented from assi- 
milating by the removal of all CO,. When the plant is exposed 
to light and turns green, the inability to assimilate exercises 
a more injurious influence upon the chloroplastids, and hence 
finally upon the entire plant, than if they remained etiolated in 
darkness. 
If green parts developed in light are prevented from exercising 
their normal functional activity by being kept in darkness, they 
also finally lose their power of assimilation. In certain cases 
this takes place with considerable rapidity. Thus, leaves of 
Phaseolus, after being for two weeks in darkness, are quite 
yellowish and can no longer assimilate. The same takes place, 
as we have seen, even in such plants as Pinus sylvestris, which 
can form chlorophyll in darkness, but is here partly a result 
of the starvation to which the seedling plants experimented 
with are finally subjected. Similar phenomena, the details of 
which have been previously given, are shown by Pellionia Da- 
veanana when the entire plants are kept for some time in 
darkness. Here also, however, the chloroplastids, partially at any 
rate, lose the power of assimilation, owing to the changes induced 
