148 ALEXANDER W. EVANS 



less convex. At the apex of the branch the few leaves which are 

 still attached bend backward almost as strongly as the underleaves. 

 After the leaves have fallen away the surface of the branch appears 

 irregularly roughened from projecting cells, but it is difficult to deter- 

 mine the actual lines of attachment. The upright leafless branches, 

 with their persistent and crowded underleaves, present a very dis- 

 tinctive appearance. Aside from P. torulosus branches of this char- 

 acter have not been noted in the Lejeuneae Holostipae. They may 

 be compared with the flagelliform branches found in Frullania Bo- 

 landeri and in the two species of Rectolejeunea noted above. 



The behavior of the caducous leaves after they have fallen away 

 was observed in but a single instance. In this case a new shoot 

 had grown out from the lower surface of the lobule not far from the 

 apical tooth. This shoot was leafy from the very base and had im- 

 mediately formed undivided underleaves as well as leaves. The 

 latter, although small, showed distinct lobules. In the few Lejeuneae 

 where germination has been observed the spore first gives rise to a 

 row of cells (sometimes very short), then to a flat thallus and finally 

 to a leafy shoot. In certain other genera the leafy shoot at its be- 

 ginning is destitute of underleaves and shows undivided leaves, even 

 though the adult shoot bears well-developed underleaves and bilobed 

 leaves. It is of interest to note that the shoot growing out of the 

 caducous leaf in P. heterophyllus showed none of these embryonic 

 features. At the same time it would be premature to draw any 

 general conclusions from a single example, and it is probable that cases 

 of more pronounced reversion may yet be discovered. It is also 

 probable that the new shoots do not always arise from the lobule. In 

 Rectolejeunea flagelUformis , where the caducous leaves lack lobules, 

 the new shoots grow out from the margin of the lobes, and it would be 

 natural to suppose that the Ptychocoleus might show the same phe- 

 nomenon. 



The lobular teeth in P. heterophyllus are usually five to seven and 

 are remarkable for their uniform structure and regular spacing. On 

 account of their being so strongly inflexed it is easy to overlook them, 

 and their features can only be made out satisfactorily by careful dis- 

 section. Each tooth consists of a single projecting cell borne on a 

 broader basal cell, and the apical tooth is indistinguishable from the 

 others except by its position. The proximal tooth, however, is often 

 less definite. The apical sinus, in explanate lobules, continues the 



