Some considerations have led me to hold a medium opinion between these two extremes. There is, in certain respects, an analogy between the medulla of plants and the nervous system of animals. It is no less assiduously protected than the spinal marrow or principal nerve. It is branched off and diffused through the plant, as nerves are through the animal. Hence it is not absurd to presume that it may, in like manner, give life and vigour to the whole, though by no means, any more than nerves, the organ or source of nourishment. It is certainly most vigorous and abundant in young and growing branches, and must be supposed to be subservient, in some way or other, to their increase. Mr. Lindsay of Jamaica, in a paper read long ago to the Royal Society, but not published, thought he demonstrated the medulla in the leaf-stalk of the Mimosa pudica, or Sensitive Plant, to be the seat of irritability, nor can I see any thing to invalidate this opinion.
Mr. Knight, in the Philosophical Transactions for 1801, p. 348, supposes the medulla may be a reservoir of moisture, to supply
