48 
However, in all the experiments where the final result has been 
favorable to the action of light I have convinced myself that a cloudy 
sky for twelve hours always showed itself in the amount of the 
absorption of oxygen in such a manner that the examination of these 
figures, noted day by day, would almost serve to show the state of 
the atmosphere during the day which preceded the observation. A 
very conclusive instance of this action is given us by experiment 
No. 4 of the second series, in which the state of the sky being care- 
fully observed it showed very marked changes. 
(3) ‘The accelerating influence exercised upon seeds exposed to: the 
action of light during the day did not stop at night; it continued to 
act in the dark with an equal, sometimes even with a greater intensity. 
T will cite as examples experiments Nos. 3, 4, 6, 7, and 8, when obser- 
rations made twice a day, morning and evening, allowed of examin- 
ing the fact I state. How can we explain this persistent action of 
light? One hypothesis only can be admitted. A portion of the 
action of the light absorbed by the grain during the day is stored up 
by it and used by it at night to accelerate its respiration. The proof 
of this is that the differences of elevation [or quantities of absorbed 
oxygen| shown in the morning by the instruments for seeds kept in 
the dark are always below those shown by the instruments and plants 
in the hght. The influence of the ight, then, continues for a certain 
time, at least several hours, even after the light itself has ceased to 
act; on the other hand, however, this action is not exerted immedi- 
ately. There is one other phenomenon that we have demonstrated 
by our experiments. Suppose the sky to be very clear; the differ- 
ences in favor of light are only apparent after two or three days 
and become much more marked toward the end of the experiment ; 
that is to say, in proportion as the daily action of sunlight is more 
and more frequently repeated. 
(4) I should. also call attention to still another peculiarity, VIZ, 
that the differences in the quantities of oxygen absorbed in the dark 
and in the hght were generally much oreater at the beginning of 
these researches than in the later experiments, and particularly in 
those of the second series. The temperature appears to me to be the 
only element that varied in these experiments. a there- 
fore be a more intense respiratory action exercised by light at low 
temperatures, and this influence would become weakened at high tem- 
peratures. This fact would be in entire agreement with the demands 
of physiology. It is easy of comprehension that a scarcity of heat 
should be counterbalanced by the action of Hght, which furnishes 
for the reaction of the respiratory organs the force that they could 
not obtain from an insufficient temperature. On the contrary, when 
the heat is intense the intervention of the light is no longer neces- 
sary, the first cause being suflicient to excite the process of germina- 
tion in the protoplasm of the seeds. 
(5) This action of hght seems to differ a little according as it acts 
upon seeds containing ‘albumen or those without albumen. In the 
ase of the albuminous seeds of the castor-oil plant the advantage was 
much more apparent in favor of those exposed to the light, “which 
advantage appeared to me much less decided for the seeds without 
albumen, such as the haricot bean. Nevertheless, as the experiments 
were not invariable in their results, the cause of the variations ob- 
