570 DR. A. J. EWART ON ASSIMILATORY INHIBITION. 
the leaves grow quite large in a few days, becoming finally of 
almost normal size, remain normal in colour, and possess an active 
power of assimilation. The trace of CO, here present and assi- 
milated exercises a kind of medicinal tonic effect, the main growth 
of the leaf being due to the supply of plastic material from 
the reserve stores in the tuber, the plant, as a whole, losing 
in weight. 
Experiments with other tuberous plants gave similar results :— 
Hyacinth.—In darkness at 20° C. to 25° O. for two months. Leaves 
12-14 em. long, in smaller side-shoot 4 to 5 em. Larger shoot in CO,- 
free air exposed to light. In 4 days is fairly green, in 1 week is fully 
green (side-shoot in air is in 4-5 days quite green, more rapid because 
younger). Chloroplastids in both after 1 week normal green, and show 
an active evolution of oxygen, about equal in the two cases. After 3 weeks 
the shoot in CO,-free air shows in parts a yellowish tinge and, on exami- 
nation, no evolution of O; but in one leaf a faint power of assimilation 
is still present. On returning to normal air this leaf and a few others 
remain living and recover; the rest turn yellow and slowly die. 
Turnip.—Etiolated leaves 5-12 cm. long, exposed to light in CO,-free air. 
By 2nd day are green to yellowish green, and show, on examination, an 
active evolution of O. Leaves, outside in air, of same age turn green at the 
same rate; but young leaves 4—5 cm. long turn green quicker than older 
ones 10-15 em. long. After 4 days leaves inside 12-15 cm. long begin 
to turn yellow, and show no evolution of O. After 1 week younger leaves 
5-8 em. long are also yellow to yellowish green, and all show no evolution 
of O. On escaping to normal air all the yellowish leaves die. If after 
4 days they are exposed to normal air, almost without exception all the 
leaves recover and show active assimilation, though some of the older 
leaves at first showed no power of evolving O. 
Beet-root.— Etiolated leaves in CO,-free air. In 2 days yellowish, and in 
2-3 days fairly green (about as rapidly as in air); but a slight yellowish 
tinge remains. Fairly active evolution of O. Lamina grows and broadens 
perceptibly after 4 days, but remains thin and imperfectly expanded. At 
end of 15 days are from 5 by 2 cm. to 4 by 1:5 em. Older leaves begin 
to twist and curl, are slightly yellowish greeu, and show no assimilation. 
Young leaves very slight yellowish or brownish tinge; assimilation very 
weak or absent. On exposure to normal air nearly all the leaves remain 
living, lamina broadens, increases, turns deep green, and shows active 
assimilation ; but in some of the older leaves the lamina in parts or 
almost entirely withers and dies. 
The foregoing results show clearly that an etiolated leaf can 
turn green and acquire an active power of assimilation if exposed 
to light in an atmosphere free from CO, in which the chloro- 
plastids are prevented from assimilating. Sooner or later, 
according to the specific nature of the plant experimented with, 
the assimilatory powers begin to decrease and finally cease. The 
cessation may take place when the chloroplastids are, to all out- 
