1894.) The Evolution of the Hepatice. oo ae 
the sporogone terminal on the main stem or on a branch. 
The line of this character that is best known is perhaps that 
leading up to the Trigonantheze from Zoopsis to Cephalozia. 
From the simplest thallose structure, differing only slightly 
from alge, the various species of Zoopsis become developed 
so as to present the successive modifications of a leaf of a 
single cell, a leaf of two cells, and a leaf of four cells; from 
these steps the passage is easy to such simple two-toothed 
decurrent leaves as we see developed in some of the Cepha- 
lozias, especially in our common Cephalozia multiflora. The 
fruiting characters in this series are so strikingly alike that 
they have even been united in a single genus. 
ot Perhaps no single group presents so many modifications 
in the diversity of foliar structure as is manifested in the var- 
lous genera of the Jungermaniales. With nothing but leaf 
cells forming a more or less well developed lamina, the great- 
est conceivable variety of form coupled with modification 
arising from environment has been differentiated, and we 
find numerous examples of marvellous adaptation of means to 
end. From these we may note the simple tripartite leaves 
of Blepharostoma made up of simple rows of cells; the intri- 
cately divided leaves of Trichocolea and Ptilidium which give 
to the species of those genera their peculiar tomentose ap- 
pearance; the ciliary fringes of endless variety that character- 
ize the numerous species of Plagiochila; the median lamina 
of Schistocheila recalling a similiar development in Fissidens 
among the true mosses, and above all the innumerable para- 
Phyllia of Stephaniella, often covering the entire surface of 
the leaf. These merely indicate a few of the possibilities of 
the foliar development. In the leaf cells themselves, we have 
‘very grade of compactness, varying from the lax structure 
of Cephalozia, Chiloscyphus and Kantia to the close compact 
structure of Herberta and Gymnomitrium. oe 
a beyond all these are the various forms of compiicts . 
the ow Clearly adapted to serve as retainers of moisture. ra "s 
"ae imple folds in the leaves of Radula, Scapania and Diplophy 
pa 
y metimes elaborately differentiated, and the water sacs of 
Jubula, Frullania and more especially Polyotus in which — 
ote Sometimes developed in great profusion. As might ‘ 
ii, these peculiar foliar adaptations for holding mo!st- 
“€ Most prominent in those species that have been driven 
