443 



1. A gonidial layer is present whose special function is that of 

 assimilation. This is, however, not conclusive, since all apothecia 

 with a thalloid exciple contain gonidia (algae), and therefore aid 

 in the process of assimilation. 



2. The extreme variability in the size and form of the pode- 

 tium indicates that it belongs to the vegetative portion of the plant 

 rather than the reproductive portion. Constancy in size and form 

 is peculiar to the organs of reproduction. 



3. The association of a large primary thallus with a small po- 

 detium and, vice versa, di small primary thallus (or none at all) with 

 well developed, much-branched podetia seems to indicate that the 

 podetium is specially adapted to supplant the function of the pri- 

 mary thallus. 



4. Cladonias with highly developed podetia {C.furcata, C. rangi- 

 feri7ia, etc.) are quite generally sterile (devoid of apothecia) and 



with primary thallus rudimentary or wanting. It would be absurd 

 to consider such plants as reproductive organs since their prime 

 function is vegetative. 



Reinke admits that the podetia are phylogenetically derived 

 from apothecia and thus in part agrees with Krabbe. The follow- 

 ing are the main reasons for assuming that this is the case : 



1. Podetia are developed endogenously from the gonidial zone 

 of the primary thallus, similar to the apothecia. 



2. Podetia have a radial structure similar to apothecia and 

 apothecial stalks. This is in sharp contrast to the dorsiventral 

 structure of the primary thallus. 



3. The apothecia occur upon the podetia. An apparent ex- 

 ception is met with in C. miniata in which the apothecia seem to 

 be sessile upon the upper surface or margin of the primary thallus. 

 In this case the podetium has become much reduced, while the 

 primary thallus has become much enlarged. 



The general conclusion at which Reinke arrives is that tJie po- 

 detium is a true liclien-thallus pJiylogetietically derived from the 

 apotJiecium. 



