228 DROSERA ROTUNDIFOLIA. Cuar. IX. 
become inflected, are not excited to further move- 
ment by bits of meat placed on the glands, until 
some considerable time has elapsed. It is generally 
believed that with animals and plants these vapours 
act by arresting oxidation. 
Exposure to carbonic acid for 2hrs., 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 sub- 
jected for two hours to this gas and then immersed in 
a solution of the carbonate of ammonia is much re- 
tarded, so that a considerable time elapses before the 
protoplasm in the lower cells of the tentacles becomes 
aggregated. 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 pre- 
sume, to the excitement from the access of oxygen. 
These inflected tentacles, however, could not be ex- 
cited for some time afterwards to any further move- 
ment by their glands being stimulated. With other 
irritable plants it is known* that the exclusion of 
oxygen prevents their moving, and arrests the move- 
ments of the protoplasm within their cells, but this 
arrest is a different phenomenon from the retardation 
of the process of aggregation 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, 
