252 THE AMERICAN NATURALIST. [Vor. XXXIV. 
of our California lichens,! that the algal cells invested or pene- 
trated by fungus filaments try by frequent division to produce 
cells which shall be quite free from contact with hypha. The 
contact of the hypha exerts an irritation which induces more 
frequent division, and at a smaller size than normally takes 
place in gonidia not in contact with hypha..  Gonidia may fre- 
quently be found in the lichen thallus, large and wholly free 
from contact with hypha.. These gonidia divide less frequently 
than the others and are by all means nearest the typical algal 
cells of the same species in size, color, form, thickness, and 
composition of wall,etc. These free gonidia are fed with water 
and mineral salts, are protected against drought and certain 
other dangers, and may really benefit by being enclosed in a 
mass of fungus hypha. Gonidia which are not merely loosely 
enclosed in the lichen body but are tightly invested if not pene- 
trated by hyphz, although they may be supplied with food 
materials and may be protected, are also robbed of part of the 
food they elaborate and are actually irritated by their associate. 
That they are ultimately sucked dry by the fungus I have 
recently shown in the paper already referred to. 
In an increasing number of lichens it is being found that the 
hypha not merely closely invest the gonidia, thereby making 
possible the osmotic movement of elaborated food from alga to 
fungus, but that the hyphz actually penetrate the gonidia by 
haustoria. These haustoria either apparently merely penetrate 
the cell-wall, pushing back the protoplasm, or they actually 
penetrate the protoplasm also. Where it is possible to demon- 
strate in any species of lichen that haustoria actually occur in 
the gonidia, there can be no doubt that the association is of 
unmixed injury to the alga, and of unmixed benefit to the 
- fungus. The movement of aqueous solutions through the haus- 
toria from the gonidia to the hyphze is different, however, only 
slightly in degree and not at all in kind from that which takes 
place between gonidia and closely clasping hyphal branches. 
The absorption of food is easier, the parasitism more perfect 
and more evident, when haustoria connect hyphz and gonidia 
1 Peirce, G. J. Loc. cit. 
