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A KEY TO THE SPECIES AND PRINCIPAL VARIETIES OF 
CLADONIA OCCURRING IN NEW ENGLAND. 
Lincoln Ware Riddle. 
One of the most urgent needs in the study of lichens at the present time 
is a set of keys to the larger genera. So far as I am aware no key to the New 
England species of Cladonia has ever been published. It is to contribute 
toward filling this need that the following key is here offered. It is based on 
the study of an extensive series of specimens, and has been tested by 
several students, both inexperienced and experienced. Yet, in a genus 
where the species are as variable as in Cladonia and where such puzzling 
transitional forms occur, it is not to be expected that any key can be con- 
structed that will serve for the determination of all specimens. It is 
hoped, however, that with material which is fairly typical, satisfactory 
results may be obtained. For the authors and synonymy of the species 
given, reference may be made to the alphabetical list at the end of the key. 
Sect. I. Primary thallus presistent and crustaceous. Podetia short (mostly 
under i cm.), club-shaped, simple or branched, apothecia pale brown, 
poorly developed C. papillaria. 
Sect. II. Primary thallus squamulose when present, often disappearing. 
Sub Sect. I. Squamules when present medium-sized to small, whitish on 
under side. (For Sub-Sect. 2. see end of key). 
Series i. Apothecia red. (Rarely the species of this series may have \ 
pale yellowish-brown apothecia, a condition known as var. ochro- 
carpia). 
A. Podetia cylindrical, without cups. 
B. Green to yellow, smooth to warty, never sorediate. 
C. Simple below, sparingly branched above. 
D. Podetia reduced, squamules of thallus sorediate 
C cristaiella v. palitdicola. 
DD. Podetia well developed, thallus not sorediate. 
E. Podetia with few squamules or none C. cristatella, 
EE. Podetia densely squamulose C. cristatella v. vestiia. 
CC. Podetia branched throughout C. C7'istatella v. ramosa. 
BB. Grayish, powdery-sorediate. 
C. Thallus scanty, podetia rarely squamulose. 
D. Podetia stout, sparingly branched, KOH + , . . . C macilenta. 
DD. Podetia slender, simple, KOH — C. bacillaris. 
