302 Evans .— Vegetative Reproduction in Metzgeria . 
influence can only be overcome with difficulty. The result is that a robust 
and mature thallus usually produces no gemmae whatever. Whether the 
species in which gemmae are unknown are able to produce them before 
they have completed their embryonic life is an interesting problem which 
can only be solved by experiment. It has already been suggested that 
M. fruticulosa may perhaps represent a juvenile stage of M. conjugata. If 
this is proved to be the case, then the influence of the apical region in 
this remarkable plant must be regularly overcome before the complete 
differentiation of the thallus has been reached. 
Some writers recognize a second antagonism between the production 
of gemmae and the development of sexual organs, based on the fact that 
gemmae are usually more abundant on sterile individuals. Correns (’ 99 , 
p. 449) has shown, however, that this antagonism is more apparent than 
real in the Bryales, and the same thing seems to be true of other Bryophytes. 
The development of sexual organs, as he notes, is associated with a late 
stage in the differentiation of the gametophyte, while gemmae, as has just 
been shown, are often produced before the late stages are reached, and 
sometimes cease to be formed afterwards. It follows from these observations 
that the sexual organs make greater or more special demands upon the 
gametophyte than the gemmae. The sterility of gemmiparous plants is 
therefore due to the fact that they often fail to reach the stage of develop¬ 
ment which can meet the requirements necessary for the development of 
sexual organs. The occasional occurrence of both gemmae and sexual 
organs on the same individual also indicates that there can be no strong 
antagonism between them. 
Yale University. 
Literature cited. 
Boatman, Nana B. (’ 92 ): The genus Metzgeria in the United States, with notes on the asexual 
reproduction. Bull. De Pauw Sci. Assoc., i, pp. 1-4. 
Cavers, F. (’ 03 ): On Asexual Reproduction and Regeneration in Hepaticae. New Phytol., ii, 
pp. 121-33, I55-65- 
Correns, C. (’ 99 ): Untersuchungen iiber die Vermehrung der Laubmoose durch Brutorgane und 
Stecklinge. Jena. 
Evans, A. W. (’ 04 ): Hepaticae of Puerto Rico. IV. Odontolejeunea, Cyclolejeunea, and Prionole - 
jeuttea. Bull. Torrey Club, xxxi, pp. 183-226, pi. 8-12. 
- (’ 06 ): Hepaticae of Puerto Rico. VI. Cheilolejeunea , Rectolejeunea , Cystolejeunea , 
and Pycnolejeunea. Bull. Torrey Club, xxxiii, pp. 1-25, pi. 1-3. 
—-(' 09 ): Notes on New England Hepaticae. VII. Rhodora, xi, pp. 185-95. 
Goebel, K. (’ 82 ): Die Muscineen. Schenk’s Handbuch der Botanik, ii, pp. 315-401. 
