86 ELEMENTS OF PLANT ANATOMY. 
1. Foliaceous Hepaticae. 
These develop in all cases from a four-sided apical cell hay- 
ing one outer wall and three inner, which form a triangular 
pyramid. In all cases except one, Haplomitrium, these plants 
are dorsiventral, this cell being so arranged that one of the 
three inner walls is parallel to the substratum. The projection 
of the apical cell on a plane at right angles to the substratum is 
therefore a triangle whose base is parallel to it. Irom the seg- 
ments of this cell formed by walls parallel to the bases arise the 
amphigastria, or ventral leaves, when they are present. When 
not present, their place is occupied by the club-shaped glandular 
hairs. From the segments above arise the ordinary leaves, 
thus arranged in two rows. In those plants which possess the 
amphigastria the projection of the apical cell forms an equilat- 
eral triangle ; in those where these are wanting or imperfectly 
developed, the triangle is isosceles, with the shorter side for the 
ground line or base. In this way the character of the plant 
may be discovered from the apical cell alone. 
The leaf consists in all cases of a single layer of cells with 
no distinction of blade and petiole. The shape varies, though 
there is a general tendency to a bipartate form. The stem is 
small and of simple structure. A few of the outer layers are 
composed of cells with somewhat thickened walls, forming ‘a 
rind, while the cells within this are larger and have thinner 
walls. The manner of branching is varied, but the axillary 
branching common to higher plants very seldom occurs here. 
2; oMasei 
The protonema, from which the true moss plant arises, dif- 
fers from that of the hepatics in several ways. It is generally 
a large, much-branched, filamentous body, which may give rise 
to several moss plants instead of one. It is usually short-lived, 
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