94 



CASSELL'S POPTJLAH GARDENING. 



drawn ty Ijotamats tietweeii "true roots," or sucli as 

 are the direct prolongations or branches of the 

 radicle of the seedling, and "adventitious roots," or 

 those which are developed only indirectly from the 

 seedling plant, and are produced from the "stem, in 

 some cases from the leaves or other parts of the 

 plant. The distinction hetween " tap-roots," as of a 

 radish (Fig. 38), in which the body of the root or of 

 the root-stock is relatively large, being developed 



Pig. 38.— Tap-root o£ Eadish. 



as a holdfast, or as a store-place for nutritious 

 matters, and the fibres are comparatively few, and 

 '' fibrous roots," as those of a grass (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 simple form 

 we meet with such a root in the common Duckweed 

 of our ponds, Zeinna (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-hairs" 

 and " root- fibrils." Eoot-hairs, though very general, 

 are not of universal occurrence; root-fibrils art 

 always present, and though sometimes destitute of 

 hairs, generally 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 subdivision of the 

 constituent cells, not exactly at the tip, but just 

 above it. Here it is a mere aggregation of minute, 



Pig. 39.— Pibrous Ecots of Grass. 



closely-packed, globular cells, rich in protoplasm, 

 and therefore highly endowed with \ital 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 be 

 seen by the naked eye in the Duckweed, but usually 

 requires the use of a powerful magnifying-glass to 

 detect it. This cap fits on to the tip of the slender 

 root-fibre like a thimble on the point of a finger. 

 This illustration, however, would be very misleading 

 without further explanation. The thimble is put 

 on the finger, but has no connection with it; the 

 root-cap is the direct production of the tip of the 

 root itself, some of the cells of which are told off 



