_ 1888. | ‘. BOTANICAL GAZETTE. 35 ee 
point for his researches. Previous experiments had forcibly suggested 
- that observed differences in the assimilative energy did not in any way ; 
depend on differences in the number of chlorophyll-bodies, or on the iy 
abundance of chlorophyll within these, but on the oxygen respiration of : 
the protoplasm. This point Pringsheim sought further to investigate. 
It has been long known that the green cells can break up CO2 in the 
absence of oxygen, where the COQ2:is mixed with some innocuous vgs. 
It is also known that protoplasmic movement is dependent on the a 
presence of oxygen. If this be so, the protoplasmic movement ina green 3 
assimilating cell, in a medium free from oxygen, should notcome toa stand- , 
stillas long as it is illuminated,and the conditions of carbonic dioxide anal- i 
ysis fulfilled. With these facts in view, Pringsheim tried by experiment to ; 
answer the question whether a plant normally assimilating would cease 
to assimilate, without any alteration of its chlorophyll relations, if it were oes 
deprived, even for a short time, of the oxygen which is essential for res- 
piration and plasmic movement, and whether it would recommence to © 
_ assimilate whenever fresh oxygen was supplied. His experiments 
answered this in the affirmative. 
The naked terminal cells of Chara leaves were placed in suspended 
drops in a microscopic gas chamber; oxygen was, as far as possible, ex- 
cluded, a continuous stream of CO. and hydrogen passed through, and 
the amount of light caused to vary. In darkness the rotation of the pro- 
toplasm gradually ceases, the length of time before stoppage varying with 
oxygen. 
But it is also a fact that the same phenomena of inanition occur when 
_Cells in similar circumstances are kept continuously in the light. Repeat- 
_ Ing the above experiment with continuous illumination instead of dark- : 
hess, Pringsheim again observed the stoppage of rotation, and with it the 
__» Sessation of the liberation of oxygen. The absence of free oxygen 1s again 
__ the condition of the cessation of function; if a small quantity be intro- 
ae duced the life revives, at least if inanition has not gone too far. ae 
___ How is this to be explained in terms of the generally accepted theory 
” 
