STUDIES AMONG OUR COMMON HEPATICAi. 79 



able to absorb and retain water for the plant's use. The stems are 

 pinnately branched, usually in a regular manner, and their branches 

 in turn give rise to similar secondary branches or branchlets. 



The leaves of our Porella (Figs. 2-5) are somewhat complicated 

 both in form and in manner of attachment, and in studying them it 

 will be found most satisfactory not to dissect them from the stem, but 

 to leave them attached and to dissect away the neighboring leaves and 

 underleaves. In this way the shape and the line of insertion of the 

 leaves can be clearly made out It will be best also to study the stem- 

 leaves rather than those of the branches, because it is in these that the 

 leaf characteristics are best developed. When we examine an intact 

 stem from above we see what are apparently closely imbricated, 

 incubous leaves. When we look at it from below, we see these same 

 leaves at the edge ; we see also the large underleaves in their usual 

 ventral position, but we see in addition what are apparently two more 

 rows of smaller leaves, one on each side of the underleaves. Upon 

 making dissections in the way described, it will be seen that these 

 apparent leaves, although independently attached to the stem, are 

 likewise attached to the structures seen from above by an extremely 

 short fold or keel, so short indeed that it is sometimes difficult to 

 demonstrate it at all. The leaves of Porella are in fact very deeply 

 and unequally bilobed, but the lobes, instead of being in one plane as 

 were the lobes in our other types, are folded together at the short keel 

 and come to be closely appressed to each other Leaves showing this 

 peculiarity are found in many genera of leafy hepatics, and are said 

 to be " complicate-bilobed." The larger of the two lobes, which in 

 this case is the dorsal, may be referred to simply as the "lobe," while 

 the smaller or ventral lobe may be called the "lobule." In Porella 

 platypJiylla the lobe is strongly convex and is almost orbicular in out- 

 line; at the rounded apex it is more or less decurved and its margin 

 is nearly or quite entire ; close to the keel it is often irregularly folded 

 or crispate, but is not really toothed. The lobule is shorter and nar- 

 rower than the lobe and is ovate in outline with reflexed margins; it 

 also is usually entire, but sometimes bears an acute tooth close to the 

 base. Both lobe and lobule are somewhat decurrent and are attached 

 to the stem by sharply and narrowly curved lines of insertion, with the 

 curves directed forward. The cells (Fig. 6) of both lobe and lobule 

 have better developed trigones than any we have yet met with, but are 

 otherwise similar to those oi Jungerviannia barbata. As we approach 

 the margins, the cells become smaller and show thicker walls than 

 those in the middle. 



The underleaves (Figs. 3-5) are so large that they sometimes 

 overlap each other; they are broadly orbicular in outline, rounded at 



