DR. A. J. EWART ON ASSIMILATORY INHIBITION, 561 
3 weeks’ etiolated seedlings of Hordeum distichum and Avena sativa. Shoots 
yellow, chloroplastids pale yellow ; no power of assimilation after | day in 
light at 15° C. (overcast January sky). Slight greenish tinge, and in parts 
very faint evolution of O. On 3rd day most leaves green, and show 
fairly to quite active evolution of O; few yellow or yellowish green, and 
show weak or no evolution of O. 
Zea Mays.—Seedling from large corn. (a) Stem 25 em. Ist leaf ll em. 
and yellow, 4 cm. exposed and deep yellow. No evolution of O. After 
14 hours’ exposure to light leaves quite green, but evolution of O is only 
moderately active, later quite active. (b) Older plant with 1 nearly full- : 
grown and 1 half-grown leaf. Both quite yellow, but no evolution 
of O. (c) Still older plant. Stem 40 em. Ist leaf withered. 2nd leaf, 
apical half brown, basal part pale yellow and living ; chloroplastids small, 
no assimilation. In light this half remains yellow and finally dies. 3rd 
leaf large, yellow and expanded. No assimilation. In light is greenish; 
on 8rd day shows weak evolution of O, fairly green and fairly active 
assimilation by 5th day. 4th leaf, partly enrolled and enclosing younger 
leaves, yellow slightly deeper, and chloroplastids slightly larger, but shows 
no assimilation. In light is in 1-2 days distinctly green and shows 
moderately active evolution of O. 5th leaf enclosed and yellowish, also 
shows no assimilation. 
j 
The inability of the etiolated chloroplastids in these plants to 
assimilate seems at first sight to be due to the small size of thẹ 
seed and consequent deficiency of nutriment (sugar), causing a 
decreased formation of etiolin, or directly affecting the develop- 
ment of the assimilatory powers of the chloroplastids, especially 
as a slight power of assimilation might be present but be masked 
by the concomitant respiration. It is found, however, that equal 
weights of etiolated leaves of Zea and cotyledons of Helianthus 
and Cucurbita yield alcoholic extracts of etiolin of about the 
same relative strength; and microscopical examination of the 
etiolated chloroplastids detects no perceptible difference in 
either their form, condition, or depth of coloration sufficient to 
explain the presence of the power of assimilation in the one case 
and its absence in the other. Palladin * found that 10 days’ 
etiolated leaves of seedling wheat contained plenty (0:85 
gramme ^/,) of sugar; but on examining such leaves, and also 
those from 14 days’ old plants, no power of assimilation can be 
detected. The etiolated seedling leaves of such grasses are unable 
in darkness to acquire the power of assimilation, not owing 
to any deficiency of nutriment or lack of etiolin, but as a direct 
effect of the absence of light, inhibiting the attainment by the 
chloroplastids of their normal functional activity. 
* Palladin, * Ergrünen und Wachsthum der etiolirter Blatter,” Ber. d. D. Bot. 
Gesell. ix. 1891, p. 229. 
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LINN, JOURN.—BOTANY, VOL. XXXI. 2s 
