Fink: Classification of Lichens 
119 
attached fungal hyphae, but Schneider thinks that these are not 
the primordia of any well-known higher lichens. Hicks (67) 
found that if a piece of bark supporting Chlorococcum is kept 
under glass in a moist place, the groups of algal cells seem to 
become transformed into a felted mass. We now know that the 
same thing is often observed in nature, lighter felted masses often 
appearing where Chlorococcum has been growing. Microscopic 
examination shows that the color change is due to the develop- 
ment of lichen hyphae. These hyphae appear more commonly 
when the alga grows near some lichen, and it may take years for 
the felted, mycelial masses to develop into mature lichen thalli. 
We have observed, in our laboratory with our students, minute 
Nostoc colonies, germinating Collema spores, other Nostoc col- 
onies penetrated by one or more germ tubes of spores, and various 
stages of development of Collemas, all growing together. When 
first parasitized by the lichen, the Nostoc colonies are of normal 
form ; but as the lichen develops within, the algal colonies become 
greatly modified in form. The Nostoc colonies are usually para- 
sitized when only 50 to 200 mic. in diameter. 
Likewise, Schwendener (119) records finding free Nostoc 
colonies, others penetrated by several C ollema-Wkt. hyphae, young 
but undoubted Collemas on scarcely modified Nostoc colonies, 
and older Collemas on much modified Nostoc colonies, all grow- 
ing together in the field. He also found similar relations between 
Leptogium subtile (Schrad.) Koerb. and Nostoc colonies, between 
a species of Placynthium (Racoblenna) and Rivularia, between 
Ephebe pubescens (L.) Fr. and Sirosiplion, and between Spilo- 
nema paradoxum Bor. and the same alga. Kny (72) recorded 
finding Lichina pygmaea Ag. and its algal host, Rivularia nitida, 
growing in proximity in the same clusters, in some portions of 
which the Riznilaria individuals were all free, in others all para- 
sitized by the lichen, and in still other portions, partly free and 
partly parasitized. 
Bornet (33) found Trentepohlia umbrina forming the algal 
host of Opegrapha varia Pers. and also growing on the branches 
of trees about the lichen, but separate from it, both on the outer 
surface and within the periderm. Toward the margin of the 
