368 MR. A. J. EWART ON ASSIMILATORY INHIBITION. 
equilibrium only when it contains less oxygen and more CO, 
than it normally does, and hence arises the readiness with which 
prolonged experimentation under these conditions may produce 
asphyxiation in a non-assimilating tissue. 
HEAT AND ASSIMILATION. 
In investigating the effects of heat upon any plant function it 
is at once necessary to distinguish between dry heat and moist 
heat, the effects of dry heat being only possible to investigate on 
plants which can withstand desiccation. 
Effects of Desiccation and Dry Heat. 
The fact that the majority of seeds and spores can with- 
stand even prolonged drying over sulphuric acid without being 
markedly affected is well known ; and Schréder* has placed on 
record an exhaustive series of observations upon the resistance 
which many vegetative plants show to similar desiccation. This 
resistance is shown by certain Hepaties (Corsinia, Lunularia, 
Marchantia); but in a more marked degree by certain Mosses 
(Barbula muralis, Bryum cespititium, &c.), Lichens (Sticta, 
Cladonia, and Evernia), and Protophyceæ ( Nostoc, Scenedesmus, 
Hematococcus, &c). Jumelle’s experiments also show that 
many mosses, lichens, &c. must possess considerable powers of 
resistance to dry heat and desiccation. 
After collecting a number of plants of sufficient resistant 
power to desiccation, a series of preliminary heating experiments 
with mosses, of which the subjoined table is illustrative, were 
made. The plants were first air-dried, next dried in a desiccator 
for a day or two, and then placed in an oven for six hours and 
kept at a given constant temperature. The plants are then 
revived in a damp chamber, and leaf preparations from all parts 
made with Bacteria to test for assimilation, as well as being 
examined by plasmolysis before or after the presence or absence 
of assimilation has been ascertained. 
The table very clearly shows that six hours’ heating is too 
short an exposure to produce a marked inhibitory after-effect 
upon the function of assimilation. It is only when the tempe- 
rature is extremely high that a complete and prolonged inhibition 
of assimilation is produced, and in such cases the greater number 
* Schróder, Bot. Untersuch. Tübingen (Pfeffer), Bd. ii. Heft 1 (1886). 
