Evans: TAXONOMIC STUDY OF DUMORTIERA 169 
(21, p. 6) he definitely recognized D. irrigua as a species, basing 
his observations on Italian material and emphasizing the impossi- 
' bility of uniting it with D. hirsuta, and in 1897 (23, p. 78) he listed 
D. irrigua from Japan. In the same year (24, p. 842) he listed 
both D. nepalensis and D. trichocephala from the Hawaiian Islands. 
In his revision of Dumortiera, published in 1899 (25), he recognized 
the validity of D. hirsuta and D. trichocephala but included D. 
nepalensis and D. irrigua among the synonyms of D. hirsuta. 
This revision apparently represents his latest views. In it he 
restricted D. trichocephala to Asia and Oceanica, citing specimens 
from Tonkin, Birma, Java, Tahiti and Samoa, as well as from the 
Hawaiian Islands. He ascribed to D. hirsuta a much wider 
distribution, giving as localities many of those mentioned above 
and also the following: Mexico, Jamaica, Guadeloupe, Colombia 
and Brazil; Reunion; Nepal and Java; Tahiti; Ireland. 
The divergent views of Schiffner and Stephani and the changes 
which these views have undergone‘are no more perplexing than 
some of the views advanced by other writers. They indicate 
that the characters distinguishing D. hirsuta, D. irrigua, D. 
nepalensis and D. trichocephala must be either untrustworthy or 
difficult to apply. The characters upon which Askepos brevipes, 
Dumortiera velutina and D. calcicola are based are likewise less 
satisfactory than might be desired and arouse the suspicion that 
variable and inconstant peculiarities have been too strongly em- 
phasized. At the same time, as will be shown below, definite 
evidence has been presented that certain differential features 
may be transmitted from one generation to another, but whether 
these features are specific in value or merely indicative of varietal 
or racial differences is exceedingly difficult to determine. Even 
if they are regarded as specific, it must be admitted that the species 
of Dumortiera are much less clearly defined than those of most 
genera of the Marchantiaceae; they are little more than “small 
species,” as this term is now employed in the literature of the 
bryophytes. 
The characters most emphasized by writers, in distinguishing 
the various species of Dumortiera, have been drawn from the size 
and method of branching of the thallus; from the structural 
features of its upper surface; from the structure and configuration 
