1895.] Vegetable Physiology. 751 
a well executed chromolithographic table. The value of this method 
rests on the fact that aerobic motile bacteria cease to move as soon as 
oxygen is withdrawn, and again become motile when a trace of it is 
added. This method of showing the photosyntax of chlorophyll-bear- 
ing cells is very delicate and exceedingly simple. A round green algal 
spore is placed on a slide in the center of a drop of water containing 
some aerobic actively motile bacterium and imprisoned by an ordinary 
cover glass cemented to the slide air tight by vaseline. If this prepa- 
ration is now examined immediately, the bacteria will be found uni- 
formly distributed through the drop and actively motile. They pay 
no attention to the green spore because they find sufficient oxygen 
everywhere. If the slide is now placed in the dark the movement of 
the bacteria gradually ceases with the exhaustion of the oxygen, and 
in this condition also the bacteria pay no attention to the algal cell. 
If, however, such a slide be left exposed to the light, the bacteria begin 
in a minute or two to swarm around the green spore and continue to 
do so as long as it is exposed to the light. Under these conditions 
there is a zone close to the spore and about as wide as the diameter of 
the latter, crowded with actively motile bacteria, a much wider zone 
in which there are only a few organisms swimming about, and a remoter 
zone of uniformly distributed non-motile bacteria. If now the mirror 
of the microscope be shaded so as to let barely enough light through 
for seeing, all self motion ceases and the bacteria which have crowded 
into a narrrow zone around the green spore begin to be distributed 
through the liquid uniformly by molecular movements. When bright 
light is flashed in again, active movement begins immediately, center- 
ing around the spore, and the two zones are reproduced, but if only a 
moderate amount of light is let in, only a small amount of oxygen is 
given off, only a few bacteria become motile, and these crowd back the 
rest forming a narrow clear zone of motile organisms, bounded by a 
crowded quiet zone, bounded in turn by a clear quiet zone, outside of 
which the bacteria are evenly divided. If a little more light be let in 
the number of motile organisms around the green spore increases, the 
inner clear zone widens, and finally with full light we have immediately 
the first condition, viz., a dense swarming mass of organisms around 
the algal cell, next a wide zone having in it only occasional rods, all of 
which are motile, and farther away a uniform distribution of organ- 
isms, which are non-motile because they have not felt the influence of 
the oxygen given off by the green spore. The algal cell of course gets 
from the bacteria CO, in return for the oxygen. Beautiful results can 
be obtained with threads of Cladophora, Spirogyra and other alge, and 
