230 ABSOKPl'ION OF LIQUIDS THROUGH HOOTS. 



substance could afterwards be discovered in the water on the 

 out.side. The apparatus lined with its colloidal film, containing 

 a small amount of saccharine solution, and surrounded bv a very 



/ &/ 



dilute aqueous solution of mineral matters, is an instructive 

 imitation of a vegetable cell. 



ABSORPTION OF LIQUIDS THROUGH ROOTS. 



617. Submerged aquatics may absorb with their whole surface. 

 They are bathed in dilute saline solutions containing the gases 

 essential to vegetative activity, and the materials for their food 



c^ / * 



can be taken from the medium surrounding them, perhaps quite 

 as well by one of their parts as by another. This fact is well illus- 

 trated by the larger algae, in which the organs popularly called 

 roots are merely mechanical hold-fasts, and the work of absorp- 

 tion can proceed at an}' part of the frond. The simplest differ- 

 entiation of organs for absorption is met with in the rhizoids or 

 complex root-hairs of mosses, and in the filaments of fungi whicli 

 bury themselves in a nutrient substratum. Above the mosses 



/ 



the differentiation of organs into roots for absorption, and stems 

 for the support of the assimilative tissue, is very plain. For our 

 present purpose it is best to begin an examination of the absorp- 

 tion of liquids by plants with a study of the structure and the 

 office of the root. 



618. It has been shown in Part I. that the younger parts of 

 the root are clothed with extremely delicate epidermal cells, 

 which, with the slender trichomes associated with them, con- 

 stitute the absorbing apparatus of the plant. (These epider- 

 mal cells of the root, taken collectively, have been called the 

 Epibleina. 1 ) 



619. The root-tip with its protective cap does not share to 

 any great extent, if indeed at all, in the work of absorption ; 

 and yet to the soft, spongy, rounded mass of tissue forming the 

 root-tip w r as formerly given the name of spongiole, on account 

 of its spongy nature, and its supposed office of sucking up nu- 

 trient matters from the soil.' 2 



1 This term, early introduced, was retained by Sehleiden : Principles of 

 Scientific Botany, 1849, pp. 68, 218. 



2 Thus De Candolle, in his Physiologie Vegetale, 1832, p. 41, says: "La 

 succion des racines s' execute par des points speciaux qu'on nomine spongioles, 

 qui sont composes (Tun tissu cellulaire tres-fin et toujours noinvau, puisque les 

 racines s'alongent sans cesse par leur extreniite. Le liquide de la terre tend 

 a entrer dans les meats de ce tissu : I. par la force de capillarite ; II. par 



