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DR. A. J. EWART ON ASSIMILATORY INHIBITION. 571 
ward appearances, quite normal and green, when, if the exposure 
has not been too prolonged, perfect recovery may, as a general 
rule, take place. Finally, the chlorophyll turns yellow or 
brownish; and when this has taken place recovery is for the 
most part no longer possible. 
The different power of resistance which the leaves of different 
plants show is primarily due to the hereditary nature of each 
given plant, but is also dependent upon the age, condition, and 
morphological character of the leaf, the supply of food-material, 
and the readiness with which the latter is available for the 
nutrition of the former. Fleshy leaves, such as those of the 
Hyacinth, are more resistant than more thin and membranous 
leaves. This is probably owing to the fact that traces of CO, 
may reach the assimilatory cells from the more or less non- 
chlorophyllaceous inner tissues of such leaves, and perhaps by 
longitudinal conduction also along with the transpiration-current 
from the underground parts. Hence very fleshy plants (Cactacee, 
Crassulaces) are probably extremely resistant in this direction, 
especially bearing in mind Meyer’s* observations that such 
plants can evolve oxygen and hence assimilate in the absence of 
CO, if exposed to light, by the decomposition of certain organic 
acids commonly present and formed abundantly in darkness. 
Leaves which remain small when grown in darkness are the 
most sensitive to exposure to light in an atmosphere free of CO,. 
The reason is that the growth, attainment of functional activity, 
and maintenance of the same in such leaves is much more closely 
dependent upon their assimilatory activity than it is in leaves 
which can attain their full normal size in darkness. A full 
account of this question is given by Jost f. 
That the phenomena above described are not due to the pre- 
vention of assimilation by the absence of CO, causing the leaf to 
be starved, has already been clearly shown by Vochting (l. c.) and 
Jost (l. c.). In the following experiments, however, with seed- 
lings the effects of starvation and of the prevention of assimilation 
work conjointly. 
* Meyer, ‘ Landwirth. Versuchsst.’ 1875, Bd. xviii. p. 410, 1878, Bd. xxi. 
p. 277; and ‘ Die Sauerstoffanscheidung fleischiger Pflanzen,’ 1876; and also 
Aubert, “ Recherches sur la Respiration et l'Assimilation des Plantes grasses," 
Revue générale de Botanique, 1892, pp. 421 & 558. 
+ Ludwig Jost, * Ueber die Abhangigkeit des Laubblattes von seiner Assimi- 
lations-Thatigkeit," Pringsh. Jahrb. xxvii, 1897, p. 403. 
