INFLUENCE OF TEMPERATURE ON VEGETATION. 725 
soon as they have been gathered ; but that it is necessary to wait for some hours till they 
have acquired the temperature of the room. (Further details will be given elsewhere.) 
M^Nab found that a large specimen of Lycoperdon giganteum produced a rise of temper- 
ature of 1-2° (F. or G.?). Bot. Zeitg. 1873, P- 560. 
CHAPTER III. 
GENERAL CONDITIONS OF PLANT-LIFE. 
Sect. 7. The Influence of Temperature on Vegetation^ can only be 
investigated scientifically by observing the influence of definite and different degrees 
of temperature on the separate vital phenomena of plants, i.e. on the various pro- 
cesses of assimilation and metastasis, of diffusion, of growth, of the variations in the 
turgidity of the cells and tension of the tissues, of the movements of protoplasm 
and irritable organs and of those endowed with periodic motion, &c. 
The determination of the facts which have here to be investigated depends on 
an accurate determination of the temperature of the plant in any given case, or rather 
on that of the part of the plant in question on which the experiment is to be made. 
This is often attended with great difficulties, and is sometimes almost impossible. 
Independently of the changes of temperature, usually inconsiderable, caused by 
respiration in the interior of the plant, the temperature of each cell depends on 
its position in the mass of tissue and on the variations of the surrounding tem- 
perature. A constant interchange of heat is going on between the plant and 
its surrounding medium by conduction and radiation which essentially determines 
the temperature of any part of a plant at any particular time. 
In reference to the conduction of heat, it must be mentioned in the first place 
that all parts of plants are bad conductors ; the differences of temperature between 
them and the air, earth, or water that is in contact with them become only very 
slowly adjusted in this way. The conductivity for heat is probably also always 
different in different directions ; that in the longitudinal direction in dry wood bears 
the proportion to that in the transverse direction of e.g. 1-25 : i in the Acacia, Box, 
and Cypress, of i-8 : i in the Lime, Alder, and Pine. 
The radiation of heat is on the other hand a very frequent and rapid cause of 
changes of temperature in most parts of plants ; the chief effect of these changes 
being to bring about differences between the temperature of the surrounding medium 
and that of the plant, especially when the parts of the plant are of small size but 
have a large hairy surface, as is the case with many leaves and internodes. It 
must be noted in this connection that the radiating power of a body is equal to its 
For more detailed proofs see my Handbook of Experimental Physiology, p. 48 et seq. 
