286 
Notes . 
But it is obvious that since the protoplasm was thus manifesting 
active vitality, respiration must have been also going on, and the only 
possible explanation of the process seemed to be that as fast as the 
carbon dioxide was produced, as the result of respiration, it was split 
up and the oxygen liberated by the chlorophyll-granules under the 
influence of the daylight. The oxygen thus would be again rendered 
available for purposes of continued respiration. Blackman’s 1 re- 
searches have shown that it is highly probable that during active 
assimilation, no carbon dioxide passes out from the leaves, but that it 
is decomposed and utilized as fast as it is produced. The observation 
just recorded seems to confirm his conclusions on this point in a 
striking manner. Of course it is quite possible that a certain small 
amount of the gases may pass out along with the hydrogen-stream, 
but enough oxygen remains to allow of respiration being maintained. 
Clark’s investigations 2 have, moreover, shown that a very low pressure 
of oxygen (about 1-3 mm. of mercury) is sufficient to enable proto- 
plasmic movement to go on. 
If the apparatus be covered over by a dark box, so as to exclude 
the light whilst the experiment is still proceeding, the movement of 
the protoplasm entirely ceases in a time varying in different experi- 
ments from two to five minutes, but it recommences on the light 
being once more admitted. This interference — the result of with- 
drawal of light — can be repeated many times, and recovery takes place 
as often afterwards. This seems to furnish a strong argument in 
support of the explanation of the phenomena here put forward, for it 
can be easily proved (in a control-experiment) that the mere ex- 
clusion of light from the leaf, the protoplasm of which is in a state of 
movement, produces no obvious effect so long as ordinary air is 
circulating through the apparatus. 
Again, in the case of hairs which do not contain chlorophyll, the 
presence or absence of light makes no difference as regards their be- 
haviour when exposed to an atmosphere of hydrogen. All movement is 
arrested, usually in a period varying from two to five minutes. I may 
add that the hairs present in the throat of the corolla of the White 
Dead-Nettle ( Lamium album) are very suitable objects on which 
1 Experimental Researches on Vegetable Assimilation and Respiration, Phil. 
Trans. Vol. clxxxvi (1895), B. 
2 James Clark, Ueb. d. Einfluss niederer Sauerstoffpressungen auf d. Bewegung 
d. Protoplasmas. Ber. d. deutschen bot. Gesellsch., vi (1888). 
