168 Henry R. Ycates. 
these circumstances little credence can be given to the supposition 
that the present distribution is due to the dissemination of spores 
through the agency of wind. Moreover, in many dioecious species 
the production of spores appears to be on the decline. The writer 
has frequently found patches of Metzgeria furcata composed entirely 
of female plants and although perfectly developed calyptras were 
present, these, upon microscopic examination, were found to contain 
only masses of disintegrated matter. Whenever the mature 
sporophyte has been met with, the plant bearing it has been 
associated with others of the male sex. /This circumstance seems 
to point to the conclusion that Metzgeria cannot produce spores 
parthenogenetically. One other circumstance has struck the writer 
very forcibly, and that is the very great variation in the yield of 
antheridia by Metzgeria. In 1904 the yield was exceedingly prolific, 
in the succeeding year at the same season hardly an antheridium 
could be found. The present dispersion and distribution of Metzgeria 
furcata cannot possibly be due to the sexual act; but is solely due 
to the production of thallidia and the ease with which they are 
detached from the parent structure by mechanical agencies. The 
attachment of the marginal thallidia to the parent structure is so 
slender that they are readily separated by currents of water and 
conveyed from higher to lower levels on the same tree trunk and 
from one tree to another when the circumstances of environment 
are suitable. In this way the writer is able to account for the 
presence of Metzgeria being more prevalent on the trunks of trees 
at the bottom of wooded glens than upon those higher up on the 
flanks on either side. 
The widespread tropical genus Dumortiera irrigua has a very 
limited distribution in Europe. It occurs only in this country in 
Devonshire, and very sparingly in Fairlight Glen, Hastings. At each 
of these stations the plants occupy specially ideal situations both as 
regards shelter and shade and where the water constantly drips 
from overarching rocks. The writer has had the plants at the 
Hastings station under periodical observation for some years but 
has failed to meet with the sexual organs in a mature state. They 
reach a certain stage of development and then drop off. In 1906 
Dr. A. Gepp showed the writer specimens bearing mature female 
receptacles which had been procured in Devonshire. If, however, 
the writer’s information is correct, the production of mature sexual 
organs, so far as the plants in this country are concerned is a matter 
of rare occurrence. 
