Page:Journal of botany, British and foreign, Volume 9 (1871).djvu/299

 ABSTRACT OF RESEARCHES ON THE ANATOMY OF BUD-SCALES. 275

most part, on the upper side, corresponding to the inner in tlie bud- scale.

A peculiarity, which has nothint^ corresponding to it in leaves properly so called, is the anatomical ditierence which exists most frequently between the inferior and protected part of the bud-scales and their upper and naked portion. The external scales being wholly naked, it is only at their lowest portion, where they are attached to the stem of the bud, that they present any difference from the upper portion ; in all the other scales this distinction exhibits itself throughout the whole p7-otec(ed portion. Speaking generally, the cellular tissues of these portions resemble those which compose the stem in its earliest state in the bud; they are more tender, and have their walls thinner than in the upper portion. Even when the internal structure of the bud-scales is only composed of a kind of liber, with vascular bundles, as in the Beech, this holds true, at least as to the delicacy and thinness of the cell-walls. In other respects, the differences may involve either the colour of the cell walls, and even the cell contents, or the structure of the cellular tissues. In these two cases the modifications go on augmenting from the base of the bud-scale to the apex, and they are more manifest on the outer side than on the inner. The difference of colour depends ordinarily on the changes which the cell contents undergo : the lower part of the scale contains cells with colour- less cell walls, and cell conteiits fre(|ueiitly containing chlorophyll, but often colourless and muddy-looking ; but in the upper part these are transformed into a sap often brilliantly coloured (Tilia, Salix), or into a brown and resinous substance, which infiltrates and tinges the cell-walls either of the epidermis alone or of the rest of the cellular tissue as well {^Rhamnus alj/iud, L.).

In so far as the difference between the upper and lower part of the scales depends on the cellular tissues, the former may consist of cork or bast fibres, while the latter resembles more the stem within the bud. However, the different structure of the bud-scales at different heights does not always correspond to the cellular tissues of the stem and that of the lower part of the scale; frequently the cellular tissue of this,. as, for example, in many conifers, consists of a layer of cork (^Abies excelsa, De Cand.), or is even transformed, for the most part, into a viscous matter {Ulmus inoitana, Sm ). On the other hand, there are bud-scales {Msculiis, Fraxinns) where there is no noticeable difference betv een the two portions, and this is especially the case with those in which the cellular tissue contains chlorophyll, and the function of warmlh-retaining seems to belong to the epidermis.

The variety in the iiuier structure of the bud-scales depends upon the fact that it is sometimes one, and sometimes another, of the cellular tissues of the stem which forms the principal portion.

It is only the tissues, however, existing outside the cambium of the stem which contribute, in a considerable extent, to the formation of buil- scales ; the cambium and the vascular bundles, although they are never wholly deficient, are always little developed. In fixing our attention on the exterior bud-scales, and on the upper and naked portions of' the iimer bud-scales, we shall find that their principal portion may consist of the following cellular tissues : —

1. Bud. — It is only the bud-sealcs of Fagus si/Ivalica, L., that consist wholly of bast ; in other cases bast bundles arc found, in addition to

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