I902 Toothwort 309 



of solution, such as transitory starch and sugar, and the 

 various substances derived from carbon assimilation which 

 are being conveyed to the different points of growth. Into 

 this fluid the haustorium plunges, and from it the protoplasm 

 of the cells composing it derives materials for growth. Now 

 it is evident that the fluid, elaborated though it be and fitted 

 for the nourishment of the tree in which it circulates, cannot 

 without some preparation be suited for the nourishment of 

 the toothwort. This, in great measure at least, is effected 

 by the cells composing the haustorium in their individual 

 act of living. We have a closely analogous case in the 

 growth of the embr3^o. The cotyledons grow at the expense 

 (^f the endosperm provided for the nourishment of the embryo, 

 and after elaboration convey it back to the point of growth. 



Lastly, we have growth by absorption of nutriment 

 by the roots. 



Toothwort, not having the means of manufacturing organic 

 matter out of inorganic, must, like animals, make use of those 

 organisms which have the power. Here, in the place where 

 it commonly grows, there is an abundant supply of matter 

 that originally was woven together by the energy of the sun, 

 for the soil is almost entirely composed of the decaying re- 

 mains of green-leaved plants that have lived and died. It 

 is this matter that it is the function of the roots to absorb, 

 and to fit it for assimilation to build up the tissues of the 

 plant. The active agents in this function are the root-hairs. 

 These are tubular prolongations of single cells of the epi- 

 dermis, open at the end next the root, closed at the end 

 nearest the substance to be absorbed. The whole structure 

 is surrounded by a very delicate and elastic wall of cellulose 

 extremely permeable by water. This is lined by a very thin 

 layer of nucleated protoplasm. The interior being filled 

 with cell sap, osmotic pressure keeps the structure tense. 

 For osmosis is the means of transmission employed ; but 

 this osmosis is very different from osmosis in a laboratory, 

 where a dead membrane or other lifeless substance is em- 

 ployed. Here the filtration is through a living membrane, 

 the cells composing which are in full active life and have 

 control of the osmotic process, for nothing can enter the 

 cell sap without traversing the living protoplasm. We know 



VOL. I. — NO. 4. X 



