-6 4 - 



from marginal cells is apparently rare and has not been seen by the writer. The 

 new plants of B. nudicaulis, so far as observed, arise singly and are essentially 

 like those of B. denudata. 1 



Although the regenerative process just described is usually first initiated in 

 leaves that have fallen away, this is by no means invariably the case. Several 

 instances have been noted in which leaves, while still attached to the axis, have 

 given rise to new plants. Leaves of this character have been situated on plants 

 in which the growing points have been injured. The inhibitory influence on re- 

 generation exerted by the growing points has thus been removed, just as it nor- 

 mally is when leaves become separated. 2 



In distinguishing B. nudicaulis from its allies there are three species or varie- 

 ties with which it should be particularly compared, namely, B. denudata, B. 

 trier enala, and the European plant known as " Pleuroschisma tricrenatum var. 

 implexum. " 



It has already been shown that the species shares with B. denudata the habit of 

 vegetative reproduction by means of caducous leaves. In B. denudata, however, 

 the plants are pale and unpigmented; the leaves are slightly larger than in 

 B. nudicaulis and tend to lie in one plane, thus giving the shoots a decidedly 

 flattened appearance; the leaf-apices (in spite of their great variability) are usuallv 

 broad and rounded or truncate; and the morphological distinctions between per- 

 sistent and caducous leaves are fairly sharp. In B. nudicaidis the shoots rarely 

 appear flattened, the leaf-apices are usually narrow, and morphological distinc- 

 tions between persistent and caducous leaves are scarcely apparent. 



In its typical development B. tricrcnata is strikingly different in appearance 

 from B. nudicaulis, but certain slender forms approach the new species more 

 closely. This is particularly true of the forms occurring in the high mountains 

 of Virginia and North Carolina, and some of these are actually found mixed with 

 two of the specimens of B. nudicaulis cited above. At the same time the writer 

 has tried in vain to find any organic connection between the two, and there is 

 little difficulty in telling them apart. Aside from their persistent habit the leaves 

 of B. tricrenata are usually more or less imbricated, they narrow more abruptly 

 from a relatively broader base, and rarely spread at as wide an angle as in B. 

 nudicaulis. The underleaves, moreover, occasionally show sharper teeth, and 

 sexual branches are not infrequent. Even in cases of exceptionally poor develop- 

 ment, where most of the branches bear minute and scattered leaves, an occasional 

 stem with larger and more imbricated leaves can usually be demonstrated. 



The "var. implexum," which has not yet been detected with certainty in 

 America, has been discussed elsewhere by the writer. 3 It is somewhat larger 

 than B. nudicaulis, its leaves are often contiguous or slightly imbricated, their 

 apices frequently show two or three sharp teeth, and male branches are pro- 

 duced in some abundance. It agrees with the American plant in being more or 

 less pigmented and in reproducing vegetatively by means of caducous leaves. 



1 See Rhodora 25! 94. 1923. 



1 See, in this connection, Buch, Overs. Finska Vetensk.Soc. Forh. 62 (Afd. A, No. 6) : 2. 1920. 



■ Rhodora 25: 81-83. 1923. 



