56 



CONSTITUENTS OF THE LICHEN THALLUS 



Fig . 2 3 . Cystococcus Cladon iae 

 pyxidatae Chod. from cul- 

 ture X 8oo (after Chodat). 



of species and he designates the algae, according to the lichen in which 

 they occur, as Cystococcus Cladoniae pyxidatae, C. Cladoniae fimbriatae, etc. 

 Meanwhile Paulson and Somerville Hastings^- by their careful research 

 on the growing thallus have thrown considerable light on the identity of the 

 Protococcaceous lichen gonidium. They selected such well-known lichens 

 as Xanthoria parietina, Cladonia spp. and others, which they collected 

 during the spring months, February to April, the period of most active 

 growth. Many of the gonidia, they found, were in a- stage of reproduction, 

 that showed a simultaneous rounding off of the 

 gonidium contents into globose bodies varying in 

 number up to 32. Chodat had figured this method 

 of "sporulation" in his cultures of the lichen goni- 

 dium both in Chlorella Beij. and in Cystococcus Chod. 

 (Fig. 23). It has now been abundantly proved that 

 this form of increase is of frequent occurrence in the 

 thallus itself Chlorella has been suggested as prob- 

 ably the alga forming these gonidia and recently 

 West has signified his acquiescence in this view^ 

 Chlorella Beij. Occurring frequently on damp ground, bark of 

 trees, etc., dividing into numerous daughter- 

 cells, probably reduced zoogonidia (Fig. 23). 



Chodat distinguishes between Cystococcus 

 and Chlorella in that Cystococcus may form 

 zoospores (though rarely), Chlorella. only 

 aplanospores. He found three gonidial species, 

 Chlorella lichina in Cladonia rangiferina, Ch. 

 viscosa and Ch. Cladoniae in other Cladonia 

 spp. 



3. COCCOBOTRYS Chod. The cells of this 

 new algal genus are smaller than those of 

 Cystococcus orProtococcus and have no pyrenoid. 

 They were isolated by Chodat from the thallus 

 of Verriicaria nigrescens (Fig. 24), and, as 

 they have thick membranes, they adhere in 

 a continuous layer or thallus. Chodat also 

 claims to have isolated a species of Cocco- 

 botrys from Dermatocarpon miniatum, a. foliose 

 Pyrenolichen. 



4. COCCOMYXA Schmidle. Cells ellipsoid, also without a pyrenoid. 

 Two species were obtained by Chodat from the thallus of Solorinae and 

 are recorded as Coccomyxa Solorinae croceae and C Solorinae saccatae. 



Fig. 23'A. A, C, Chlorella vulgaris 

 Beyer. B and C, stages in division 

 ■ X about 800 (after Cliodat) ; E, 

 Chi. faginea Wille x 520 (after 

 Gerneck); F — I Chi. miniata; F, 

 vegetable cell ; G — \, formation 

 and escape of gonidia x 1000 

 (after Chodat). 



' Paulson and Hastings 1920. 



- Paulson in -litt. 



