ON THE LICHEN-GONIDIA QUESTION. 
263 
of their respective cell-contents. To the former group, that 
with bluish- green cellules, he assigns five types, viz. 1. Sirosi - 
phonece ; 2. Rivularice ; 3. Scytonemece ; 4. Nostochacece ; 
5. ChroococcacecB : and to the latter group, that with chloro- 
phyll-green cellules, he assigns the remaining three types, viz. 
6. Confervaceoe ; 7. Chroolepidece ; 8. Palmellacece. 
Such genera and species of these as live in water are of course 
excluded from the question, as it is evident that the fungus can 
have no access to them. The author also describes the occur- 
rence of these so-called algal-types in various genera of lichens, 
and makes lengthened observations upon the character they pre- 
sent and the modifications they undergo in several individual 
species. Amongst other instances adduced by him, he finds the 
hyphse entering the fronds of different algae, e.g. Sirosiphon , 
Nostoc, Glceocapsa , and encompassing the gonidia with a net- 
work; while in a certain number of genera, e.g. Roccella , 
Arnoldia, Lempholemma , Pannaria , he found them uniting 
themselves to the gonidia by an actual junction. In the con- 
clusion of his paper, he observes that the algal-nature of the 
lichen-gonidia, which he maintains has been established in the 
cases he has reviewed, is extremely probable also in every other 
case, and that consequently the gonidium, as hitherto supposed, 
is not a self-developed organ of the lichen. But though not 
thus to be regarded, gonidia would still, in a physiological point 
of view, remain as instruments of assimilation and of a sexual 
increase. Although they have not the power in themselves to 
form a thallus, they are an essential constituent of it, and are 
undeniably the most important, though not the only ministers 
of nutriment for the composite plant called a “ lichen,” inas- 
much as this is also partly furnished by means of the substra- 
tum. From this general outline of the hypothesis of Schwen- 
dener, it will at once be perceived that its adoption would 
entirely subvert all our previous notions as to the mutual rela- 
tions between the filamentose tissue and the gonidia of lichens. 
Nay, more, it would necessitate the degradation of lichens from 
the position they have so long held as an independent class, and 
in any system of classification would render it extremely diffi- 
cult rightly to dispose of the half algal, half fungal monstrosity, 
called a “ lichen.” 
Passing over several other writers who have, more or less 
directly, made contributions of greater or less importance to 
the above theory, we come to a more recent, and in some re- 
spects the most plausible advocate of the hypothesis. This is 
Dr. E. Bornet, whose extensive, and from a Schwendenerian 
point of view, exhaustive memoir upon the subject, entitled 
“ Recherches sur les Gronidies des Lichens,” appeared in 66 Ann. 
des Sc. Nat.,” 5 ser. t. xvii. (1873). In this he expands and 
