332 
STRUCTURE AND LIFE HISTORIES 
branched, coralloid nodules on their roots (Fig. 241). 
These roots are caused primarily by infection with the 
FIG. 239. Thallus and erect portions (podetia) of two species of lichen 
of the genus Cladonia. The larger podetium is proliferating, and bears a 
number of apothecia on the margin of the podetium of the first rank. 
Apothecia are also shown on the margin of the larger podetia at the right. 
(Drawn from nature.) 
FIG. 240. A lichen produced synthetically by cultivating the spores 
of a fungus in association with a green alga. The culture was carried on 
in a test-tube on sterilized culture media, thus preventing contamination 
by bacteria and foreign spores. (After Bonnier.) 
nitrogen-fixing organism, Pseudomonas radicicola. By 
the development of lenticels at the base of each nodule 
