186 * Effects of Frost on Dormant Vegetation. [April, 



Trees of the largest dimensions exhibit this difference more clearly than 

 smaller ones, and the lower part of the tree more than the upper portions. 

 The extremes of heat and cold, such as frequently occur in wiuter days, 

 in the temperature of the air, he could never discover to have occurred 

 in the interior of trees. The monthly average of the temperature of the 

 air and that of the trees corresponded, however, within the trifling differ- 

 ence of from one-tenth to three-tenths of a degree. Various kinds of trees 

 manifested the same results in this respect. He also found, from close 

 observation, that the average temperature of trees was somewhat lower 

 — from 0.74° to 0.24:° — than the temperature of the air. This he 

 ascribed to the powerful respiratory process of the leaves, whereby, in 

 conformity with well known physical laws, some degree of cold must be 

 produced. In the spring months of March and April, the temperature 

 of trees was, however, found to be higher than that of the air — 0.7° to 

 0.38°. This difference was doubtless caused by the agency of ascending 

 fluids, taken up from the earth by the roots. 



That plants partake of the heat contained in the soil, has long been 

 received as a settled principle in vegetable physiology. The benefits 

 derived from the application of hottom heat, so often exhibited in agri- 

 culture and horticulture, seem to confirm the opinion, that heat, brought 

 into the vegetable organism by the ascending fluids, must be productive 

 of a vigorous vegetation. If plants, therefore, do not possess that degree 

 of heat within themselves, which would be necessary to secure the 

 resistance against cold from without, we have, as mentioned above, to 

 look for the true cause in the mysterious and inscrutable principle of 

 vital 2:>oiuer. 



But before dropping the subject of vegetable heat, let us propound a 

 question in conclusion. Do plants possess or originate within themselves 

 no heat at all ? Our answer to this is, that they do possess some degree 

 of heat ; but it is so feeble and insignificant that it for a long time 

 escaped all scientific observation. Indeed, so minute is this develop- 

 ment, that in the single individual plant it could never have been per- 

 ceived ; but, by taking many individuals together, their aggregate 

 amount of heat is clearly appreciable and demonstrable. Tor example, 

 it has always been known that a pile of germinating seeds evolves a 

 great degree of heat ; and this has been attributed to the process of 

 incipient fermentation. Closer investigation has, however, shown that this 

 heat results, not from fermentation, but from the strongly excited vital 

 action of germination. Fermentation is significant of death, and is a 

 proce>»s of decomposition ; but this is significant of life, and is a process 

 of re-production. Besides heat, the natural products of fermentation 



