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first the tissues of the thallus swelled considerably but soon 
broke down and the residue assumed the consistency of jelly. 
The strands, freed from the acid, were stained and mounted 
in balsam. They did not break down during the process but 
remained rigid and resistant. The mounts showed the identical 
markings seen in the prepared longitudinal sections. 
As most liverworts thrive only in moist habitats, the whole 
surface, if close enough to the sub-stratum, might absorb all the 
water needed or the thallus might be provided with rhizoids 
which perform the same function. With an increase in speciali- 
zation in these forms, as erect branches or parts raised above 
the thallus surface, it would seem almost necessary to have some 
sort of conducting system, more or less complex. 
Chick and Tansley 14 say the following in regard to the three 
liverworts having conducting tissue : ' ‘ The three genera Palla- 
vicinia, Steph., Symphogyna, Nees et Mont., and Hymenophyton, 
Steph., differ in well-marked characters connected with the po- 
sition 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. The strand cells are formed, as might be expected, 
by longitudinal division of the inner cells cut off from the seg- 
ment of the apical cell and are differentiated very close to the 
apex . 7 7 
The Growth of the Thallus . — The growth of the thallus pro- 
ceeds by means of a wedgeshaped apical cell. This type seems 
characteristic of the dichotomously branching forms, for the 
cell can be divided into two segments alike in size and shape 
and like the original apical cell. As each segment cuts off seg- 
ments from its inner face the two apical cells are pushed farther 
apart, and the dichotomous branching results. Leitgeb 10 says, 
“The growth of the shoot results through the division of the 
'vertex cell , 7 which forms a four sided segment, cutting off to 
right and left and dorsal and ventral sides. We find the same 
method of growth in the segments of Aneura and Pellia and the 
leaf-building segments of Fossombronia and Frullania, The 
segments cut off from the right and left sides of the apical cell 
develop the side leaves, while those cut from the dorsal and 
ventral sides take part in developing the branches. Those on 
the ventral side form hair papillae and scales . 77 Some from 
the dorsal side form the sex organs. 
