Box— Vol. I.] PEIRCE— NATURE OF LICHENS. 227 



corresponding disadvantages. The single gonidial cell 

 must do everything itself or perish. The individual 

 gonidial cells penetrated by haustoria are no better off as 

 individuals than algal cells of the same species outside the 

 lichen : they are obviously worse off. 



Beside the gonidial cells penetrated by haustoria, there 

 are a much larger number, to be seen both in sections and 

 in free preparations, which are invested more or less closely 

 either by the hyphse themselves or by short branches there- 

 from. These last Schneider (1896a) calls " extra-cellular 

 haustoria." The true haustoria, of which we have just 

 been speaking, he terms " intra-cellular haustoria." Both 

 are branches of hyphse, are therefore morphologically the 

 same; both are organs of nutrition, are therefore physiolog- 

 ically the same; but it seems hardly desirable to give to 

 organs which do not penetrate, but only clasp, the same 

 name which DeBary (1884) and so many after him have 

 used with the original meaning only — " in's Innere der 

 Zellen dringende Seitenzweige." 



Whether we have to do with naked or enclosed masses 

 of living protoplasm, their absorption of food is by the 

 same means — by osmosis. The osmotic absorption of 

 aqueous solutions of food substances into cells enclosed 

 by thin cellulose walls is nearly if not quite as rapid as with 

 naked cells. Through a thick cellulose membrane or 

 through two cellulose membranes which, though closely 

 applied to one another, are thicker than only one, osmosis 

 is slower than through a thin cellulose membrane. Through 

 a gelatinized membrane osmosis is also slower than through 

 a cellulose membrane of the same thickness (Pfeffer 1897). 

 From these considerations we see the means by which both 

 the haustoria penetrating, and the hyphal branches invest- 

 ing, the gonidial cells obtain from them the nutrient solutions 

 which the fungus must obtain from them or die. If the 

 hyphas become gelatinized as to their walls, their absorp- 

 tion of food will be diminished equally with their loss of 

 water. The production of haustoria will, therefore, facili- 

 tate the absorption of adequate amounts of food. In many 



