170 Evans: TAXONOMIC STUDY OF DUMORTIERA 
of the receptacles; and from the size of the spores. These char- 
acters may be taken up in order. 
In its general aspects the thallus presents great uniformity. 
It consists of a flat, strap-shaped structure, with more or less 
undulate margins, and clings loosely to the substratum. Ac- 
cording to Ernst (4, p. 163; pl. 18, f. 1, 2; pl. 20, f. 18, 19) the mar- 
ginal undulations tend to be more pronounced in D. trichocephala 
than in D. velutina and are often accompanied by irregular inden- 
tations, but these vague differences are neither constant nor of 
great significance. The differences in size which have been 
described seem likewise very uncertain, although Campbell, 
(2, p. 331) in his account of D. calcicola emphasizes the narrow 
thallus, measuring barely 5 mm. in width. Quoting again from > 
Ernst (4, p. 162) D. trichocephala includes larger forms on the 
whole than D. velutina, the thallus attaining a maximum width 
of 3 cm., but it includes also forms which are no wider than those 
of D. velutina. The size seems to be very strongly influenced by 
external conditions. 
he branching of the thallus is usually dichotomous but some- 
times ventral. The sexual receptacles are terminal, the branches 
bearing them being variable in length and normally limited in 
growth. Not infrequently, however, a sexual branch innovates 
at the apex, the innovation growing in the same direction as the 
branch and broadening out from a stalk-like base. Such an 
innovation is usually found in connection with a male receptacle 
or a female receptacle which has failed to be fertilized; but even a 
sterile branch, the growth of which has been arrested in some way, 
is sometimes induced to innovate. Apical innovations in Dumor- 
tiera have commonly been regarded as somewhat abnormal, 
caused perhaps by unfavorable environmental conditions. In 
D. calcicola, where they occur more regularly, at least on sexual 
individuals, they give rise to jointed sympodial systems of very 
striking appearance and have been emphasized by Campbell 
(2, p. 334) as a_ specific peculiarity. Unfortunately similar 
sympodia have been recorded by Schiffner (10, p. 275) in speci- 
mens of “D. hirsuta” from New Guinea and by Ernst (4, p. 161) 
in specimens of D. velutina from Java, so that they are by no 
means confined to D. calcicola. 
