136 MORPHOLOGY 



Stictaceae. 



Lobaria, Sticta. 



Lecanoraceae. 



Lecania {L. lecanorina), Aspicilia^- 



Physciaceae. 



Placodium bicolor' • 



C. Algae that form Cephalodia 



The algae of the cephalodia belong mostly to genera that form the 

 normal gonidia of other lichens. They are: 



Stigonema, — in Lecanora gelida, Stereocaulon, Pilophorus robustus, and 

 Lecidea pelobotrya. 



Scytonema, — a rare constituent of cephalodia. 



Nostoc, — the most frequent gonidium of cephalodia. It occurs in those 

 of the genera Sticta, Lobaria, Peltigera, Nephroma, Solorina and Psoroma; 

 occasionally in Stereocaulon and in Lecidea pallida. 



Lyngbya and Rivularia,—ra.r&\y present, the latter in Sticta oregana^. 



Chroococcus and Gloeocapsa, — also very rare. 



Scytonema, Chroococcus, Gloeocapsa and Lyngbya are generally found 

 in combination with some other cephalodia-building alga, though Nylander* 

 found Scytonema alone in the lobulate cephalodia of Sphaerophorus stereo- 

 cauloides, a New Zealand lichen, and the only species of that genus in which 

 cephalodia are developed; and Hue^ records Gloeocapsa as forming internal 

 cephalodia in two species of Aspicilia. Bornet^ found Lyngbya associated 

 with Scytonema in the cephalodia of Stereocaulon ramulosum., and, in the 

 same lichen, Forssell" found, in the several cephalodia of one specimen, 

 Nostoc, Scytonema, and Lyngbya, while, in those of another, Scytonema and 

 Stigonema were present. In the latter instance these algae were living free 

 on the podetium. ForsselP also determined two different algae, Gloeocapsa 

 magma and Chroococcus turgidus, present in a cephalodium on Lecidea panaeola 

 van elegans. 



As a general rule only one kind of alga enters into the formation of the 

 cephalodia of any species or genus. A form of Nostoc, for instance, is in- 

 variably the gonidial constituent of these bodies in the genera, Lobaria, Sticta, 

 etc. In other lichens different blue-green algae, as noted above, may occupy 

 the cephalodia even on the same specimen. Forssell finds alternative algae 

 occurring in the cephalodia of: 



Lecanora gelida and Lecidea illita contain either Stigonema or Nostoc; 



Lecidea panaeola, with Gloeocapsa, Stigonema or Chroococcus; 



^ Hue 1910. ''■ Tuckerman 1875. 3 Schneider 1897, p. 58. ■■ Nylander 1869. 



= Bornet 1873, p. 72. « Forssell 1885, p. 24. 



