Evolution of the Collemacet. 371 | 
scarcely ever produce apothecia. They appear to be multiplied 
by the Nostoc-like gemmules excreted from the upper surface 
of the thallus, and not by any sexual propagation. And pro- 
bably fertile thalli are only evolved from spores. 
We may therefore conclude that the genus Nostoc of modern 
algology, in part at least, if not entirely, may be regarded as 
the initial or metamorphic states of the Collemata. 
i have already added to the family of the Lichenes various 
Scytonemata and Strosiphones ; and, indeed, certain Gleocapse 
(such as Synalissa picina, S. meladermia, Collema evilescens, 
and Bryophagus Gleocapsa, Nitschk., optime forte dicendus 
Glaocapsa bryophaga) may be added. 
The lichenose nature of these vegetations can only be mani- 
fested by the fructification. I have formerly stated that the 
various sterile states of them which are so abundantly met 
with are analogous to the Leprarie of the family of the Li- 
chenacei, and that Leprariz never pass into typical Lichens 
producing apothecia, but always remain leprose and sterile. 
In like manner the Nostoc-like and analogous states of the 
Scytonemata, Strosiphones, and Gleocapse remain in their 
peculiar inferior grade, atypical and sterile, without any evo- 
lution into a more perfect and fertile condition. It may be 
also suspected that not a few other vegetable forms at present 
received into algology ought to be transferred to lichenography ; 
but a fuller experience is needful to determine how far this is 
true. 
On the sandy roads about Paris and elsewhere in France I 
have observed that in a rainy season a small Nostoe often 
quickly springs up, and in the selfsame localities Collema 
pulposum in a sterile condition afterwards occurs; and we 
may hence probably infer that this derives its origin from the 
Nostoc. But the evolution of this adult Lichen, as of all 
others, is slow. 
It may also be noted that the age of Lichens may be best 
determined in cemeteries, where they abundantly occur on 
sepulchral stones bearing the dates of their erection, and upon 
which, no doubt, the Lichens, everywhere abundant, speedily 
disseminated themselves. Thus the specimens would coincide 
in size with the varied ages of such stones. For example, 
in the cemetery outside the city of Helsingfors, I have noticed 
that it required a period of twenty years for a Lichen (a com- 
mon Physcia) to attain to a moderate or adultsize : consequently 
their growth must be excessively slow. 
26* 
