Page:Proceedings of the Royal Society of London Vol 1.djvu/280

Rh The medulla in this case appeared to be wholly inactive.

By an examination of buds which had been inserted in a preceding summer, or attached by grafting in the spring, it appeared that vessels diverged from them into the bark of the stock.

It seems therefore probable, that a pulpous organizable mass ﬁrst derives its matter from the bark or albumum, and that this matter subsequently forms the new layer of bark; for if the vessels had proceeded as radicles (according to Darwin’s supposition,) from the inserted buds or grafts, such vessels would be different from the natural vessels of the stock; neither is it probable that vessels could extend, by actual addition to their extremities in the course of a few days, from the leaves to the roots. Mr. Knight is consequently inclined to believe that the matter itself which composes the new bark acquires an organization of vessels calculated to carry the true sap; but whether, in the ordinary growth of trees, this matter be derived from the bark or the alburnum, or from both, it will be extremely difﬁcult to determine. This, however, is certain, that bark in many cases exists previous to the existence of albumum; but there seems to be no case, in the ordinary growth of vegetables, in which alburnum exists previous to the formation of bark.

[n this paper the author relates brieﬂy some observations which he formerly made on the progressive changes of these rings, which appear to him to lead to a satisfactory explanation of their origin.

In the ﬁrst place he observed, that some species of fungi were always to be found at the exterior margin of the dark ring of grass if examined at the preper season. This position of the fungi led him to conjecture that progressive increase from a central point was the probable mode of formation of the ring; and he thought it likely that the soil which had once contributed to the support of fungi, might be so exhausted as to be rendered incapable of producing a second crop. The defect of nutriment on one side would occasion the new roots to extend themselves solely in the opposite direction, and would cause the circle of continually to proceed, by annual enlargement, from the centre outwards. The luxuriance of the grass follows as a natural consequence, as the soil of an interior circle is enriched by the decayed roots of fungi of the succeeding year’ 5 growth. Such a progressive enlargement, he remarks, had already been observed by Dr. Hutton on the hill of Arthur's Seat near Edinburgh; but Dr. Hutton had not attended to the production of