PHYSIOLOGY. 237 
that after the middle of January, with us atter the 
20th, the sap enters trees. At this period it is 
thought to descend, to be ready in the spring. But 
whoever thinks that trees, shrubs or herbs are, as 
it were, dead in winter, and without action, is much 
mistaken. I shall endeavour to,refute this opinion, 
and to represent this fact in the. Way it ought to be 
considered, | 
During the whole summer the root sends the 
food which it has imbibed by its radicles to the 
stem, and what the stem receives from the leaves 
is constantly wasted in the formation of new parts, 
till either this evolution ceases, from the strength 
being exhausted, as in annual plants, or till the parts 
above ground, which can no longer resist the incle- 
mency of the weather, become separated, as in herbs, 
shrubs and trees. With the fall of the leaves in 
ligneous plants, and with the drying of the stem in 
herbs, all their vegetating powers are exhausted. 
The great quantity of moisture which the root for- 
warded to the plant, is consumed, in trees and 
shrubs, in the formation of branches, of wood, 
splint, inner bark, leaves, blossoms and fruit, as 
well as in the growth of the root: in herbs, in the 
formation of the parts above ground, the fruit and 
the root itself. ‘These fibres, which hitherto con-~ 
veyed the food, begin to become harder, and are no 
longer able to serve this purpose. ‘The sap which 
circulates in the vessels can no longer produce new 
shoots above ground, as the temperature is unfa- 
yourable. From the moment, then, that the leaves 
of ligneous plants and the stems of herbs decay, 
the 
