No. 400, ] FUNGUS AND ALGA IN LICHENS. 251 
grew at a constant rate instead of the alga sometimes growing 
much faster than the fungus, the parasitism of fungus on alga 
would result much sooner in the destruction of each algal cell. 
As it is, the fungus destroys the algze, but only by degrees, and 
so slowly that a new generation is mature before the first is 
consumed. 
If there is osmotic transfer of non-nitrogenous food from 
alga to fungus, there may also be osmotic transfer of something 
else from fungus to alga. Presumably there is. De Bary, 
Reinke, and others say that the fungus supplies the alga with 
water and mineral salts. Undoubtedly this is true, but I doubt 
this being other than by the capillary movement of columns 
or films of water, holding mineral salts in solution, between 
and along the hyphz which, running more or less parallel with 
one another, form continuous capillary tubes from the substra- 
tum throughout the body of the lichen. By this means the 
fungus certainly does supply the alga, but so would cotton fibres 
or glass tubes similarly placed. It cannot be questioned that, 
in its position in the lichen, the alga needs to have water and 
mineral salts conducted to it, but its position is not of its own 
seeking, natural, or necessary, or at all evidently advantageous. 
In its natural habitat the alga (Protococcus, Gloeocapsa, Nostoc, 
etc.) could supply itself with aqueous solutions of needed food 
materials without the intervention of a dearly paid servant. 
It is alleged by some that what the fungus obtains from the 
alga is merely the excess of organic matter elaborated by the 
latter, and that the alga is manured by the waste substances 
produced by the fungus. Such conceptions of the physiology 
of living organisms are anything but definite. According to 
this, plant cells and plant bodies are leaky affairs from which 
nutritious substances ooze in appreciable quantities. Every one 
knows that this is not true. The ooze theory of the nutrition 
of the associates in the lichen must, therefore, be abandoned. 
It is said that, if the fungus were simply parasitic upon 
the alga, the algal cells would not so rapidly multiply, would 
not look so healthy as they often do in the lichen thallus. 
Besides the reason already given for this, it seems to me cer- 
tain, from my study of Ramalina reticulata, and of some others 
