DR. 8. O. LINDBERG ON ZOOPSIS. 208 
Pleurocarpi, on the contrary, are much more uniform than the 
Acrocarpi both as to the vegetative and to the fructificative sys- 
tem. Besides that, they show neither such high forms as Poly- 
tricha, nor such lowly developed ones as Andreææ. The nerve 
also, that very characteristic organ in the leaf of the Musci, is 
always of the same low internal organization. More difficult than 
in Acrocarpi is it to decide which of their links may take the 
first place. "This place of honour, must, I think, be adjudged to 
Thyidium, ex. gr. Th. tamariscifolium*, according to its strongly ra- 
mified stem, bearing numerous paraphylla, and divided into several 
étages of years: its leaves are of different forms, in relation to 
their place either on the stem itself or on its primary or second- 
ary branches ; all the leaves are constructed of strongly incrassate 
and papillose cells; but the bracts of the perichetium are quite 
unlike the leaves both in their form and in their areolation and 
glossiness ; the theca is also often unusually large f. 
A very remarkable fact is, that in most of the groups of Liver- 
worts and Mosses the highest form is cosmopolitan, or at least 
widely diffused. In proof may be mentioned that among Marchan- 
tiacee the M. polymorpha and, in antarctic countries, M. tabularis, 
perhaps only a subspecies of the former, are the commonest of 
all; of Jungermanniacea foliose gynomitriee, Frullania dilatata 
and tamarisci—and of J. foliose thalamomitriee, Lepidolena ma- 
galhanica and Trichocolea tomentella are rather common; Antho- 
ceros levis may with justice be called a cosmopolite. Sphagnum 
palustre has, with its subspecies, the widest diffusion of all spe- 
cles; in the same relation are, for instance, Polytrichum commune 
and juniperinum, Tortula ruralis, Funaria hygrometrica, Bryum 
roseum (and its subspecies), Mnium undulatum and rostratum, 
Gymnocybe palustris, Rhacomitrium hypnoides, Thyidium tama- 
risci-folium, Stereodon cupressiformis, &c. The same law we find 
also in many genera. Is it because all these best-developed forms 
have the strongest vital power, aud are thus best armed in the 
struggle for life ? 
* Hypnum tamariscifolium, Neck. Meth. Muse. p. 158. n. 9 (1771), =H. 
tamariscinum, Hedw. Sp. Musc. p. 261 (1801). i 
t A common law in the Mosses is, that, when the theca is regular and upright, 
the peristome is less developed, very often that of a Leskea, or theinner one want- 
ing; but when the theca is irregular and cernuous, the peristome is more highly 
developed, very often that ofa Hypnum,—thus in Funaria, most pleurocarpous 
forms, &e.; and not unfrequently both forms occur in the same species, as in 
Plagiothecium denticulatum and silvaticum. 
LINN, JOURN,— BOTANY, VOL, XIII. Q 
