. Cassell's popular gardening. Gardening. Fig. 38.—Tap-root of Radish. as a holdfast, or as a store-place for nutritious matters, and the fibres are comparatively few, and " fibrous roots," as those of a gTass (Fig. 39), though important from the point of view of form and classi- fication, is less so from that of physiology, because in both cases the essential portions, so far as regards work, are the root-fibres or feeding-roots, and of these the ultimate subdivisions only. The feeding- root, apart from all less important and variable characteristics, may be looked on physiologicall
. Cassell's popular gardening. Gardening. Fig. 38.—Tap-root of Radish. as a holdfast, or as a store-place for nutritious matters, and the fibres are comparatively few, and " fibrous roots," as those of a gTass (Fig. 39), though important from the point of view of form and classi- fication, is less so from that of physiology, because in both cases the essential portions, so far as regards work, are the root-fibres or feeding-roots, and of these the ultimate subdivisions only. The feeding- root, apart from all less important and variable characteristics, may be looked on physiologically as a mere thread of cellular tissue. In a simjDle form we meet with such a root in the common Duckweed of our ponds, Zenina (Fig. 40), but even this is not the least complex form in which the root exists, for from the surface of many roots just above their tips are pro- duced hairs of extreme tenuity, consisting only of a single cell, each one of which exercises the function of absorption, and is in this sense a perfect root. We must distinguish then between root-haii-s" and " root- ; Root-hairs, though very general are not of universal occurrence; root-fibrils arc always present, and though sometimes destitute of hairs, generall)- give origin to them. The root- fibril, or ultimate subdivision of the root, may be looked on in all cases as a mere thread of cellular tissue, growing in length by rapid subdi\'ision of the constituent cells, not exactly at the tip, but just above it. Here it is a mere aggregation of minute,. Fig. 39.—Fibrous Roots of Grass. closely-packed, globular cells, rich in protoplflsm, and therefore highly endowed with vital activity. Above, some of the globular cells show a tendency to lengthen and to become progressively modified into wood-cells and vessels. The extreme tip is very generally guarded by a little cap, which may seen by the naked eye in the Duckweed, but usually requires the use of a powerful magnifying-glass t
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Keywords: ., bookcentury1800, bookdecade18, booksubjectgardening, bookyear1884
