320 Campbell.—Studies on some East Indian Hepaticae . 
investigated. Fertile material of this form, which is very abundant in many 
parts of Hawaii, was collected by the writer during the past summer, and it 
is doubtful whether it can properly be referred to D. trichocephala. 
All of the species of Dumortiera are characterized by a more or less 
complete suppression of the air-chambers which are so conspicuous a 
feature of the thallus of the typical Marchantiaceae. In the Hawaiian form 
referred to above, no trace of the air-chambers could be detected, even in the 
youngest portions of the thallus; but in the other species more or less 
conspicuous remains of the air-chambers are visible. Ernst 1 has studied 
carefully these air-chambers in D . trichocephala and D. velutina , and the 
writer can confirm his results from an examination of material from the same 
localities in Java where Ernst collected his specimens. 
In D . velutina not only are the air-chambers very evident near the 
apex of the thallus, but the green tissue found in the air-chambers of the 
typical Marchantiaceae is represented by crowded papillate cells which 
completely cover the surface of the thallus and give it a characteristic 
velvety texture, very different from the greasy-looking, olivaceous, nearly 
smooth surface in D. trichocephala. In the latter the papillate cells are 
either completely absent or very sparingly scattered over the surface. 
In all species the epidermis is completely wanting except in the 
youngest parts of the thallus ; but the lateral walls of the air-chambers may 
persist more or less completely so as to form an irregular reticulation on 
the surface comparable to that present in the typical Marchantiaceae (see 
PL VIII, Fig. 3). 
The development of the air-chambers is, to some extent at least, 
associated with the environment. 2 When the conditions are comparatively 
dry the air-chambers are better developed than in a very wet situation, and 
excessive moisture may cause a complete suppression of the air-chambers. 
Of the species considered in th£ present paper, D. calcicola , which grows 
under relatively dry conditions, has the air-chambers comparatively well 
developed. 
That moisture is not the only factor concerned, however, is probable. 
During the past summer the writer collected two species of Dumortiera in 
Hawaii not infrequently growing together, one of which had conspicuous 
reticulations on the surface of the thallus, while the other showed no trace 
of air-chambers. 
The Reproductive Organs. 
As in other Marchantiaceae, the sex-organs in Dumortiera are borne on 
the characteristic receptacles. The male receptacle (PL VIII, Fig. 6 , H ; 
Text-fig. 2 , C) is a nearly flat disc, borne upon a very short pedicel. The female 
receptacle, or carpocephalum, is more or less conspicuously convex, and at 
2 Coker, W. C. : Selected Notes, II. Bot. Gaz., xxxvi, 1903, pp. 225-30. 
1 Loc. cit. 
