Page:An introduction to physiological and systematical botany (1st edition).djvu/115

 Rh returning from the leaf, where it has been acted upon by the air and light, forming new wood, is clearly the cause of the increase of the vegetable body. But it is not so clear how the resinous, gummy or other secretions, laid aside, as it were, in vessels, out of the great line of circulation, can directly minister to the growth of the tree. I conceive they may be in this respect analogous to animal fat, a reservoir of nourishment whenever its ordinary supplies are interrupted, as in the winter, or in seasons of great drought, or of unusual cold. In such circumstances the mucilaginous or saccharine secretions especially, perhaps the most general of all, may be absorbed into the vegetable constitution; just as fat is into the animal one, during the existence of any disease that interrupts the ordinary supplies of food, or interferes with its due appropriation. It is well known that such animals as sleep through the winter, grow fat in the autumn and awake very lean in the spring. Perhaps the more recent layers of wood in a Plum or Cherry-tree, if they could be accurately examined, might be found to contain a greater