230 ABSORPTION OP LIQUIDS THROUGH ROOTS. 



substance could afterwards be discovered in the water on the 

 outside. Tlie apparatus lined witli its colloidal film, containing 

 a small amount of saccharine solution, and surrounded by 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 vegetati\'e activity, and the materials for their food 

 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 bj' the larger algae, in which the organs populai-ly called 

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

 tion can proceed at any part of the frond. The simplest diflfer- 

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

 complex root-hairs of mosses, and in the iilaments of fungi which 

 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 tlie 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 trichoraes associated with them, con- 

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

 mal cells of the root, taken coUectivelj', have been called the 

 Epiblema.^) 



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

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

 and yet to the soft, spongj', rounded mass of tissue forming tbe 

 root-tip was 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.^ 



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

 Scientific Botany, 1849, pp. 68, 218. 



2 Thns De Candolle, in his Physiologic Vegetale, 1832, p. 41, says: "La 

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

 qui sont composes d'un tissu cellulaire tres-fin et tonjours nouvcau, puis()ue les 

 racines s'alongent sans cesse par leur extremite. Le hquide de la terre tend 

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



