ROOTS OF HEPA T ICE. 



3' 



lateral root-fibres arise from them with properties like those possessed by the lateral 

 roots of vascular plants. As the younger part only of a true root attaches itself 

 to the soil by its root-hairs, so in the roots of mosses a similar connection appears 

 at the young end only; further backwards from this, the cell- wall becomes 

 thicker, and takes on more or less the solidity, resistance, and dark colour found 

 on the older root-fibres, e. g. of Ferns and Horse-tails. Although the geotropism, 

 heliotropism and the sensitiveness to pressure and moisture in the roots of mosses 

 have not been hitherto directly investigated, it may nevertheless be concluded with 

 certainty, judging from their whole biological behaviour, that they completely resemble 

 true roots in all these respects. 



Still more simply organised are the roots of the Liverworts, especially those with 

 flat, extended, ribbon-like shoots, e.g. of 

 Marcha7itm. From the shaded underside 

 of their dorsiventral shoots, thin-walled, 

 narrow, but very long tubes appear, simply 

 as protuberances of certain epidermis cells, 

 which penetrate deep into the earth with- 

 out becoming branched. In the simplicity 

 of their anatomical structure, they resemble 

 apparently only the root-hairs of the vascu- 

 lar plants, with which, in fact, they agree in 

 so far that they, like those, are immediately 

 concerned Avith the function of nutrition. 

 These simple tubes, however, possess in 

 addition the essential physiological peculi- 

 arities of typical roots, as is to be concluded 

 with certainty from their whole behaviour ; 

 their sensitiveness to light and moisture, 

 and their origin under the influence of 

 gravitation and pressure, are beyond 

 doubt. We have before us, in the root- 

 hairs of the Marchanh'cB and other flat- 

 shooted Liverworts, organs of the simplest 

 structure, in which are united all the phy- 

 siological peculiarities of the root-hairs and 

 root-bodies of the more highly organised 

 vascular plants, as further proof that these 

 physiological properties are quite indepen- 

 dent of the cellular structure of the higher plants. The prothallia of Ferns agree 

 with the Liverworts, as regards the formation of roots, so completely, that it is 

 sufficient to refer to Fig. 21 for the elucidation of both. 



If we now turn to the Algce, we meet with great variety both in the 

 root formation, and with respect to all other relations of organisation. But the 

 Algae, with rare exceptions, live entirely in water, and can al)sorb this and 

 the food-matters dissolved in it with their whole surface ; and their roots 

 must thus be of very subordinate importance in the absorption of food, whereas 



FIG. 21.— Pro-embryo {Prothal/tu) of a Fern {Os»tiiH</a 

 alls) seen from tlie under side, a antlieridia ; iv root- 

 rs ; V the growini; point (magnified). 



