186 DROSERA ROTUNDIFOLIA. [CHAR IX. 
with animals and plants these vapours act by arresting 
oxidation. 
Exposure to carbonic acid for 2 hrs., and in one case for 
only 45 m., likewise rendered the glands insensible for a 
time to the powerful stimulus of raw meat. The leaves, 
however, recovered their full powers, and did not seem in 
the least injured, on being left in the air for 24 or 48 hrs. 
We have seen in the third chapter that the process of 
aggregation in leaves subjected for two hours to this gas and 
then immersed in a solution of the carbonate of ammonia is 
much retarded, so that a considerable time elapses before the 
protoplasm in the lower cells of the tentacles becomes aggre- 
gated. In some cases, soon after the leaves were removed 
from the gas and brought into the air, the tentacles moved 
spontaneously ; this being due, I presume, to the excitement 
trom the access of oxygen. These inflected tentacles, how- 
ever, could not be excited for some time afterwards to any 
further movement by their glands being stimulated. With 
other irritable plants it is known* that the exclusion of 
oxygen prevents their moving, and arrests the movements of 
the protoplasm within their cells, but this arrest is a different 
phenomenon from the retardation of the process of aggre- 
gation just alluded to. Whether this latter fact ought to be 
attributed to the direct action of the carbonic acid, or to the 
exclusion of oxygen, I know not. 
* Sachs, ‘Traité de Bot. 1874, pp. 846, 1037. 
