5 TUDIES A MONG O UR COMMON HE PA TICAL. 1 83 



ing a length of 2 or 3^™- and measuring with the leaves only i"^'"- in 

 width. Upon cutting thin transverse sections, it is seen that the 

 stems are built up of cells with slightly and uniformly thickened walls, 

 those of the outer layer being somewhat larger than the others, but 

 resembling them in most other respects. 



The leaves are distant or loosely imbricated, and a marked differ- 

 ence in the manner of insertion will at once be noticed between these 

 leaves and those of our two preceding types. In Lepidozia the leaves 

 are still very obliquely inserted, but the line of attachment curves in 

 such a way that the upper and not the lower margin of the leaf is 

 turned toward the apex of the stem. When the leaves are crowded, 

 this important difference becomes much more evident; for it will 

 then be seen that the upper part of each leaf lies over the lower part 

 of the succeeding leaf, and not of the preceding leaf, as was -the case in 

 Jnngerniannia and Lopliocolea. The type of arrangement found in 

 Lepidozia is called "incubous;" and as a result of it, the apical bud is 

 turned toward the ground instead of away from it and is protected 

 by older leaves which completely hide it from view. The two types 

 of leaf -arrangement which we have studied are, in nearly every case, 

 constant throughout genera and even larger divisions of the leafy he- 

 paticae. The leaves of our species are approximately quadrate in shape 

 and broaden out very little from the base. Each leaf is cleft to about 

 the middle into four obtuse or subacute lobes separated by subacute 

 sinuses, and its margins are otherwise quite entire. On slender stems 

 and branches the number of lobes is ofted reduced to three, a peculi- 

 arity which is especially frequent on rock-specimens. The cells of the 

 leaves are poh^gonal in outline and increase slightly in size toward the 

 base; all of them have thin and delicate walls without trigones. 



Underleaves are everywhere present and are much more con- 

 spicuous than in either of our preceding types. They are about half 

 the size of the leaves and are slightly wider than the stem. Like the 

 leaves, they are divided almost or quite to the middle into four lobes, 

 although on slender branches this number is reduced to three or even 

 to two. 



Attention has already been called to the regular, pinnate branch- 

 ing of the prostrate plants. The ordinary vegetative branches are 

 all lateral outgrowths from the stem ; each branch occupies the posi- 

 tion and takes the place of the lower half of a stem-leaf, while the 

 upper half of the same leaf persists as a bi-lobed structure borne 

 partly on the stem and partly on the branch. The first leaf developed 

 on a branch is an underleaf , which is somewhat pushed out of position 

 and is only two- or three-lobed, even on robust branches; the succeed- 

 ing leaves and underleaves are normal in their arrangement. 



