PREFACE. 



'^HE following memoir does not profess to be a complete monograph 

 of all known species of Cephalozia, but only a descriptive account of 

 all the species I have been able to examine. A few additional species 

 are known to me only by name, and a few others may lurk undis- 

 tinguished, or as yet unpublished, in our large herbaria ;- but the ma- 

 terial here brought together amply suffices for my purpose. I have 

 chosen this genus for illustration, because, in an extended view of its 

 limits, it comprises within itself certain characters heretofore deemed of 

 generic or even of tribal importance. Such are, 1°, the frondose, as 

 contrasted with the leafy, stem ; 2°, the succubous, transverse, and in- 

 cubous foliage; 3°, the acrogenous and the cladogenous fructification; 

 all of which modes are to be seen in the various species of Cephalozia, 

 and the two last-mentioned often coexist in a single species, or even in 

 the same individual. On the other hand, characters hitherto overlooked, 

 or underrated, are proved, by an extensive study of Hepaticae, to be 

 constant throughout large groups of species, and therefore of great 

 diagnostic value. These are 1°, the insertion of the branches on the 

 stem : either all postical, as in Cephalozia, Kantia, &c.; or all lateral, as 

 in Lejeuna, Radula, Frullaria, &c.; or some combination of these modes 

 in various other genera, the most unusual being where all the leafy and 

 the flowering branches are antical (epicladousj, and only the root-bear- 

 ing branches are postical (hypocladous), as in Anomoclada. The in- 

 sertion of the branches with respect to the leaves varies considerably in 

 different genera, but is usually constant to one type in the same genus, 

 and sometimes throughout a series of genera. Thus, the branches are 

 all exactly axillary to the sideleaves in Frullania, Scapania, &c.; infra- 

 axillary (adjacent or adnate to the outer base of the leaf) in Lejeunea 

 and Radula ; axillary to the underleaves in Kantia, &c. 2°, the origin of 

 the primary keels or angles of the perianth, which are either derived 

 from the marginal (or intramarginal) sutures of the subplane flower- 

 leaves, as in Lophocolea, Plagiochila, &o.; or else are the already exist- 

 ing angles of the complicate (or at least carinate) flower-leaves, as in 

 Cephalozia, Scajmnia, &c. 3°, the structure of the capsule-walls and the 

 number of cell-layers composing them. This is independent of the kind 



