6 Tans ley and Chick. — -Notes on the 
‘ fibrous cells whose walls become much thickened, and exhibit 
a number of shallow pits on their walls, at first view resembling 
ordinary striatum.’ He also calls attention to the discon- 
tinuity of the axile strands of the branches with that of the 
mother-axis, and explains it developmentally by reference to 
the fact that the apical cell of a branch, after cutting off a 
few segments which form short broad cells, remains dormant 
for some time before continuing its development. It is only 
after the resumption of growth that the inner cells of its 
segments undergo the frequent longitudinal divisions which 
result in the formation of the cells of the axile strand. Hence 
the latter is always separated from that of the mother-axis 
by the first-formed broad cells. 
In the hope of obtaining some information as to the con- 
ditions of the evolution of primitive vascular systems, we 
have investigated representatives of all three of the genera in 
question (the only Liverworts in which these strands have as 
yet been found), and though our observations are not so 
complete as we could desire, partly owing to the difficulty of 
getting sufficient and satisfactory material, but even more 
because of the impossibility of making a study of these plants 
in their homes — they are very scattered and nearly all tropical 
forms — yet the results seem worth putting together in this 
place. 
Of the three genera Pallavicinia , Steph., Syniphyogyna , Nees 
et Mont., and Hymenophyton , Steph., the two first are placed 
by Schiffner 1 in the Leptotheceae, the last in the Metzgeri- 
oideae, neighbouring families of Jungermanniaceae Anakro- 
gynae. They differ in well-marked characters connected with 
the position and investment of the sporogonium, and it is 
perhaps most probable that the striking character they have 
in common — the possession of an axial strand — has developed 
independently in each genus. Each of the three genera, too, 
may be divided into two sections, of which one, presumably 
the more primitive, contains species with an undifferentiated 
thin flat and creeping thallus, while in the other the thallus 
1 Engler and Prantl’s Pflanzenfamilien, i, 3 (Hepaticae), 1893. 
