MANEROGAMIA : RADICAL ORGANS. 



219 



All rooting of an axis of a bud, except that of the embryo, 

 occurs by adventitious roots. The region just below the base of a 

 leaf appears to be most inclined to the production of roots. 



In the formation of an adventitious root, a vascular bundle is 

 developed in it, issuing from the vascular bundle of the stem. 



Only in very few manuals do we find a merely indicated, in none 

 a strictly and consequently traced, distinction between roots and adven- 

 titious roots, which are so thoroughly different in their course of develop- 

 ment and morphological import. Theories of the function of the root, 

 Vegetable Systems founded on the structure of the root, endless contests 

 about nutrition, the distinction between Monocotyledons and Dicotyle- 

 dons, &c., in short, a whole literature owes its origin solely to the 

 neglect of this essential distinction. In the Monocotyledons it often 

 readily happens that the adventitious roots are exclusively observed, and 

 this led Richard to divide plants into Endorhizce (with roots which break 

 through from the interior, Monocotyledons), and Exorhizce (the roots of 

 which are formed by the mere elongation of the radicle, Dicotyledons). 

 Dutrochet, who observed the formation of adventitious roots on a Di- 

 cotyledonous rhizome (stem), opposed, at once, that all plants are en- 

 dorhizous. Both are wrong. DeCandolle discovered the cap upon the 

 adventitious roots of Pandanus, and we had directly a great theory 

 about the spongioles (spongiolce radicales\ bodies which have no exist- 

 ence ; and those caps, the cap of the root of aquatic plants and of com- 

 mon root- ends, were all thrown together under this head. Had half the 

 time which has been wasted in the spinning out of such untenable and 

 useless hypotheses been applied to fundamental investigations, in what 

 a different position would Science stand ! 



In most plants of which the radicle does not become developed, for 

 instance, most Grasses, Lemna, &c., the course of formation of adven- 

 titious roots may be traced completely even in the embryo ; more will 

 be said on this point under the head of the seed. For the others, the 

 rhizome of Phragmites communis and Nymphcea alba are to be recom- 

 mended. A peculiar structure, the physiological import of which is 

 still very obscure, the cap of the root (pileorhiza), occurs in the Lem- 

 nacece (fig. 154 156.), Pistiacece, and some other water-plants, e. g. Hy- 



154 



155 



1M Telmatophace gibba. Embryo : a, the seed ; b, the cotyledonary mass ; c, the 

 radical end, with its covercle (embryotega, Gaertner) ; d, the bud breaking forth from 

 the transverse slit of the cotyledon ; e, protuberance which precedes the issue of an 

 adventitious root. 



i55 Longitudinal section of the preceding. In the seed (a) may be distinguished the 

 testa, a thin endosperm, and the cotyledon, in the middle of which runs a vascular 

 bundle, which gives off one twig to the bud (d), and another to the adventitious root 

 (e). In the latter, the cap may be distinguished from the root itself. 



148 T. yibba. The adventitious root from fig. 155. in longitudinal section, strongly 



