94 Rhodora (June 
Under such circumstances the forking and thread-like stems, tipped 
with rudimentary leaves but otherwise naked, except for the scanty 
vestiges left behind by the leaves and underleaves, present a very 
distinctive appearance. The caducous habit is sometimes more 
marked in the leaves than in the underleaves, and leafless stems 
with persistent underleaves are occasionally found. There are cases, 
too, where an axis recovers from the caducous habit and resumes its 
growth in a normal vegetative manner. 
The caducous leaves are usually smaller than the ordinary leaves 
described above and may be reduced to a length of 0.2 mm. or even 
less, the caducous underleaves exhibiting a similar reduction in size. 
When a caducous leaf gives rise to a new stem the latter grows out 
directly, by a process of regeneration, from one of the leaf-cells, 
usually at or near the base. The stem elongates rapidly and produces 
a long series of minute leaves and underleaves, very similar to those 
on the flagelliform branches but somewhat firmer in texture and 
tending to spread more widely. Both leaves and underleaves are 
shortly bifid and essentially alike, the stem thus representing an 
almost radial structure and showing but little indication of the dis- 
tinct dorsiventrality found in the normal leafy stems. The later 
stages in the development of these new stems have not been observed. 
When typical plants of B. tricrenata and B. denudata are compared 
the differences between them are striking and have been brought out 
to a certain extent in the preceding account. In B. tricrenata, for 
example, the plants are more or less pigmented with brown, the 
stems tend to be suberect, the branches diverge at a narrow angle, 
and the persistent leaves are strongly convex; in B. denudata, on the 
contrary, the plants show no distinct brown pigmentation, the stems 
tend to be prostrate, the branches diverge at a wide angle, and the 
leaves are flat or only slightly convex and often caducous. When 
B. denudata is compared with “ Pleuroschisma tricrenatum var. 
implexum" a closer approach is apparent, but in this latter plant the 
pigmentation is still present in a greater or less degree, the caducous 
habit is less marked and the caducous leaves themselves are less 
highly differentiated. It will be noted that “ Mastigobryum ambiguum 
(in part)" is cited as one of the synonyms of B. tricrenata. This 
species was based on two specimens, as follows: * prov. Massachusetts 
(Asa Gray)" and "ad litora boreali-occidentalia (Hb. Hk.)." "The 
first specimen has not been seen by the writer but there is little 
