FINK—THE LICHENS OF MINNESOTA. 9 
Chaetomium, and Sordaria are among those which may be closely 
related to the ancestors of the fungal symbionts. Further statements 
concerning the fungal ancestry will be found in the outline of 
classification.¢ 
THE ALGAL SYMBIONTS AND THEIR RELATED ALG. 
The algal symbionts are much better understood than the fungal. 
Indeed, in the descriptions of genera in this volume statements are 
made regarding the alge to be found in each genus, and some use is 
made of these algal types in classification into families and genera. 
Fig, 1.—Algal types with associated fungal hyphe. a, Cystococcus, each cell surrounded by haustoria. 
b, Chroolepus, showing a branching chain of cells, surrounded by haustorial hyphez. c, Nostoc, show- 
ing the algal filaments and the intermingled fungal hyphe. d, Gloeocapsa, showing the haustoria and 
the fungal hyphie surrounding the algal cells. a, Enlarged 750 diameters; 6, 325 diameters; c, 500 
diameters; d, 650 diameters. From Schneider. 
The alga most commonly found in lichen thalli is of the genus Cysto- 
coccus (fig. 1, @), and this genus is closely related to Pleurococcus 
(fig. 2, d, p. 10), which itself is supposed to be the algal symbiont of 
a few common lichens. Sections of lichens of the genera Collema, 
Synechoblastus, Leptogium, and some others show chains of cells 
which are so similar to those of free-living species of the algal genus 
Nostoe that we may regard these algal symbionts as certainly belong- 
ing to that genus. Chroolepus (fig. 1, 6), an alga which may readily 
be distinguished from Pleurococcus, is the algal symbiont in a con- 
siderable portion of the crustose lichens. Other algal symbionts, 
which will be referred to only rarely in these pages, are Gloeocapsa 
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