aquatic grass, whose root is naturally fibrous and creeping,) growing with an ovate juicy bulb on the top of a dry wall. This variety has been taken for the true A. bulbosus, t. 1249, which has always bulbs even in its native marshes. We see the wisdom of this provision of Nature in the grasses above mentioned, nor may the cause be totally inexplicable. When a tree happens to grow from seed on a wall, it has been observed, on arriving at a certain size, to stop for a while, and send down a root to the ground. As soon as this root was established in the soil, the tree continued increasing to a large magnitude[1]. Here the vital powers of the tree not being adequate, from scanty nourishment, to the usual annual degree of increase in the branches, were accumulated in the root, which therefore was excited to an extraordinary exertion, in its own natural direction, downward. There is no occasion then to suppose, as some have done, that the tree had any information of the store of food
- ↑ A particular fact of this kind concerning an ash was communicated to me by the late Rev. Dr. Walker of Edinburgh. See also Trans. of Linn. Soc. v. 2. 268.
