104 FIRST FORMS OF VEGETATION. 
family, among which indeed Acharius had placed 
them ; and on the other hand by the Collemas, a soft 
gelatinous family of lichens, found in damp shady 
places, which alter their form and consistence 
very much in drying, and assume very variable 
shapes. Indeed the opinion has been recently 
expressed by Continental botanists, that these 
Collemas are only perfectly developed states 
of plants, whose young, or imperfectly developed 
forms have hitherto stood amongst the unicellular 
or rudimentary alge under distinct generic and 
specific names. Some have gone even further, 
and applied that observation to the whole tribe 
of lichens; asserting that the bud-like cells or 
gonidia of every lichen, which have the power of 
continuing to live and develop themselves even 
when separated from the thalli which produced 
them, may be referred to some species of low- 
type alga. It may also be mentioned that Mr. 
Sorby, while recently conducting researches among 
the chromatological relations of the lower plants 
and animals, has found a most interesting series of 
connecting links between olive algz and lichens 
in the colouring matters which they yielded. All 
these views countenance the opinion of Dr. Tucker- 
man, the late distinguished American lichenologist, 
who defined lichens to be “ perennial aérial alge,” 
and regarded them as due to the transformation 
