Page:Proceedings of the Royal Society of London Vol 1.djvu/348

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The object of this paper is to show, that the roots of trees are al- ways generated by the vessels which pass from the cotyledons of the seeds, or from the leaves through the leaf-stalks and bark, and that they never spring immediately from the albumum.

The radicle, which proceeds from the seed, appears to the author to differ from other roots in its mode of growth, since it elongates, by interstitial increase, like the intervals betWeen the buds in the succulent annual shoot; but roots, on the contrary, elongate only by new parts added to their extremity, and never by the extension of parts previously formed.

The proper roots, which come ﬁrst into existence, Spring from the point of the radicle ; and since there is at that time no albumum, it is evident they must arise from some other source.

At ﬁrst they consist solely of cellular substance, within which cor-

tical vessels are next generated; by these the albumum is subse- quently deposited, in the form of wedges, meeting in the centre. .. If a portion of bark be removed from a vine, in a circle, round the stem, and any wet substance be applied to it, roots are soon emitted from the upper edge of the decorticated space; and when the al- bumum dies so as to obstruct the progress of sap through it, buds are usually protruded from the lower edge, but never from the upper; -the roots deriving their matter from the ﬂuid that descends through the cortical vessels, and buds from the ascending sap.

In some varieties of the apple-tree, Mr. Knight observes, there are many rough excrescences on the trunks and branches, which. under different circumstances, form either buds or roots, and these varieties are accordingly very easily propagated by cuttings. When such ex- crescences had begun to form upon some trees of two years old, mould was applied to some of them in the spring, and roots were found to form early in the summer. But when mould was applied to other trees of the same age and variety, from which the top had been cut at a short distance above the excrescence, no roots were emitted for want of descending sap, but buds were formed instead.

The author observes, that both alburnum and bark contain true sap; but whether that which descends to form roots differs essentially from that which ascends to form buds, he thinks it nearly impossible to decide: he is, however, much more disposed to attribute the for- mation of different organs to the different action of the vessels, than to any difference of the ﬂuids from which they are formed.

After albumum has been formed in the roots, it then has the power of producing buds from its upper extremity, as well as ﬁbrous roots from its lower extremity. The continuance of the entire root in the state of alburnum, appears owing to moisture; for if the mould be taken away so as to expose part of a root to the air, that part is subsequently found to contain heart wood.

The formation of buds from the potatoe, beneath the soil, may ap—