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tion that the hypothesis has its origin, and its sole origin, in 
the resemblance of the gonidia to certain algae or pretended 
algae, and but for this it would never have been heard of. Such 
a resemblance had previously been noticed by authors, and so 
far back as 1849 Thwaites, in “Ann. Nat. Hist.,” ser. ii. 
vol. iii. p. 219, had distinctly drawn attention to the circum- 
stance. In this, however, he rightly saw but as it were a 
parallelism between the two ; for “ similarity,” be it observed, 
is neither logically nor scientifically synonymous with “ iden- 
tity.” Itzigsohn also, in “ Bot. Zeit.,” 1854, p. 521, pointed 
out the similarity of certain lichen-gonidia to free algal forms ; 
though Schwendener regards this as evidence of identity. Sub- 
sequently Nylander, in “Flora,” 1870, p. 92, when briefly 
noticing the algological theory of gonidia, very pertinently 
observes that such an unnatural existence as they would thus 
pass, enclosed in a prison and deprived of all autonomous 
liberty, is not at all consonant with the manner of existence of 
the other algse, and that it has no parallel in nature, for nothing 
physiologically analogous occurs anywhere else. He also asks 
what prevents the gonidia of lichens presenting forms and a 
structure similar to algae (or the gonidia of algae ?) as in certain 
specified instances, and yet both remain distinct classes of vege- 
tation, noticing as a case in point that although chlorophyll is 
nearly similar in mosses, ferns and phaenogamics, no one has 
ever on that account united them in one and the same class. 
The more accurate view to be entertained of those algae which 
have the appearance of gonidia is, he observes, to regard them 
at least partly as being in reality not algae, but erratic lichen- 
gonidia vegetating abnormally. This is the view taken also by 
Krempelhuber, who holds that there are no conclusive reasons 
against the assumption that the lichen-gonidia may be self- 
developed organs of the lichen proper rather than algae, and 
that these gonidia can continue to vegetate separately, and so 
be mistaken for unicellular algae. So also Th. Fries, 1. c. says 
that it is likely that various modern families of “ algae ” con- 
sist of lichen-gonidia growing free, which ought therefore to be 
excluded from the system of algae. Again, in “ Obs. Pyr. Or.” 
1. c. Nylander argues that were the hypothesis true, “ Lichens 
would grow best and occur most abundantly in places where 
those algae which are regarded as the gonidia of lichens abound, 
and would there also be observed to be crammed with these 
elements.” On the contrary, however, he affirms (and the ex- 
perience of all field-lichenists will verify the assertion) that 
“ lichens avoid these stations, which are not inhabited except 
sparingly by Collemacei and a few others, which are not always 
well developed, and which do not contain any such algoid- 
gonidia in their texture.” Moreover, he adds (p. 47) that “ so 
