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division, in folding, and in the development of remarkable structures known 
as water-sacs. The simplest type of leaf is that which is undivided, 
although this is probably not the most primitive type. In this case the leaf 
varies in form from ovate to broadly rotund, and in all our northern genera 
is rounded or bluntly pointed at the apex {Figs. /-?). The margin is com- 
monly entire but is more or less toothed in certain species of Plagiochila 
{Fig. 4). The leaves here and throughout the group are sessile just as in 
the mosses, but the line of attachment instead of being transverse is usually 
oblique; sometimes the forward or apical end of this line is turned toward 
the substratum and sometimes away from it, these conditions being best 
shown by such diagrams as Figs. 3 and 6, the arrows indicating the direc- 
tion of growth. These differences in the attachment of the leaves bring 
about differences in the way in which they overlap each other and are of the 
utmost importance in distinguishing certain genera. The condition seen in 
Fig . 3 is known as succubous and is found in the common genera Junger- 
mannia, Nardia, Chiloscyphus, Plagiochila {Fig. 4) and Odontoschisma 
{Fig. 3). The other condition is called incubous {Fig. 6), and is found in the 
common Kantia Trichonianis {Figs. /, 2). The distinction between succu- 
bous and incubous leaves applies not only to species with undivided leaves 
but also to many of those with variously lobed or divided leaves. 
Among lobed or divided leaves the simplest condition is found where 
only two apical teeth or lobes are present: sometimes the teeth are very 
minute and only one or two cells long: in other cases the divisions 
extend to the middle of the leaf or beyond. Among species with succubous 
leaves the bidentate or bilobed condition is found in the genus Cephalozia 
{Fig. 7), and in many species of Lophocolea {Fig. 8) and Lophozia ; it is much 
rarer in species with incubous leaves but is clearly shown by Kantia Sul- 
livantii {Fig. 9). In Lophocolea heterophy lla the leaves show all gradations 
between the deeply bilobed and undivided conditions. 
Tridentate and trifid leaves, quadridentate and quadrifid leaves are also 
found among the Hepaticae; none of our northern species, however, show a 
larger number of primary lobes than four. In the genus Bazzania the 
leaves are incubous, and in our commonest species, B. trilobata {Fig. 10 ), 
have three apical teeth. In Lepidozia reptans {Fig. //), also with incubous 
leaves, the same stem will often produce both trifid and quadrifid leaves; 
the same is true of the succubous leaved Lophozia harbata and of other 
species of this genus. Here again gradations between bifid leaves and those 
just considered are also to be observed. 
All of the leaves which we have so far noted are more or less flat- 
tened in one plane, The form of the leaves, however, is much more difficult 
to understand when the lobing is accompanied by folding. This condition is 
described as “complicate,” the fold being called the “keel.” We find it 
most frequently among bilobed leaves, which are then described as “ com- 
plicate-bilobed.” In these leaves the method of attachment is entirely dif- 
ferent from what we have described above, each lobe being attached 
independently to the stem . and the two lines of attachment meeting at an 
angle, which is sometimes very sharp. In the genus Marsupella {Fig. 12), 
