Page:An introduction to physiological and systematical botany (1st edition).djvu/49

 Rh the stem of a tree, as in the plum or cherry, and because it is found to be cracked wherever an unnatural excrescence is produced on the bark. No doubt the cuticle is formed so as to accommodate itself only to the natural growth of the plant, not to any monstrosities, and those lumps cause it to burst; just as it happens to ripe fruits in very wet seasons. Their cuticle is constructed suitably to their usual size or plumpness, but not to any immoderate increase from too great absorption of wet. If the cuticle be removed from any part, no swelling follows, as it would if this membrane only kept the tree in shape.

The extension of the cuticle is astonishing, if we consider that it is formed, as Grew well observes, on the tenderest embryo, and only extended during the growth of the plant, and that it appears not to have any connexion with the vascular or living part of the vegetable body. But though so accommodating in those parts where it is wanted, on the old trunks of most trees it cracks in every direction, and in many is entirely obliterated, the old dead layers of their bark performing all the requisite offices of a cuticle.