442 
the number of branchings. In cross section the podetium is seen 
to have a radial structure, hollow, bearing a gonidial zone just 
within the outermost protective (cortical) covering. The assimi- 
lative surface of the podetium is usually much greater than that 
of the thallus-lobe, from which it took its origin. Both Krabbe 
and Schwendener * look upon the two distinctive forms of thallus 
as a species of alternation of generation. Wainio + believes that 
the apothecial stalk is converted into a vertical thallus by a form 
of metamorphosis. A similar view is held by Reinke; that is, the 
podetium was originally an apothecial stalk (perhaps comparable 
to that of the Caliciaceae and of Bacomyces) which finally became 
metamorphosed into a true thallus. This metamorphosis was of 
such a nature that the increase in size and assimilative function of 
the podetium corresponded to a decrease in size and function of 
the primary thallus. : 
The author enters into a more detailed discussion of the mor- 
phological characteristics of the leading types of Cladoma for 
the purpose of illustrating the structural modifications of the 
podetium and its relation to the primary thallus and apothecia. 
Life-size figures of the types accompany this discussion. Reinke 
quite frequently speaks of “ fertile forms” when only “ pycnidia” 
are present, which shows conclusively that he considers these 
structures as reproductive organs coequal in importance to the 
apothecia. The fact that the pycnidia (and spermagonia) may 
occur on either the primary thallus or the podetium, while the 
apothecia occur on the podetia (excepting a few C/adonias which 
are said to have no podetia or only pseudo-podetia) does not seem 
to raise any question in the author’s mind as to the feasibility of 
considering the former as true sexual organs. This is only in 
passing, but it is well to remember that sexual organs are gener- 
ally not so variable in their occurrence and position on the vege 
tative portion as the pycnidia and spermagonia evidently are. 
Without going into further details the following summary may 
be given of Reinke’s reasons for assuming that the podetium is 4 
thallus rather than a reproductive organ. : 
zur Wissenschaftlichen Botanik, 2: 169. 1860. 
} Wainio, Monographia Cladoniarum Universalis. Helsingfors, 1867. 
