146 MOSSES AND FERNS chap. 



pact thallus without intercelluar spaces (D. cichoraceus) , while 

 in others these are very much developed and the thallus has a 

 more or less spongy texture, e. g., D. Javanicus. The develop- 

 ment of the thallus and sporogonium has been studied by Leit- 

 geb ( (7), v., p. 39), and in the main corresponds very closely 

 to Anthoceros. A difference may be noted, however, in some 

 details. Thus the form of the apical cell is like that of Pellia 

 epiphylla, where the inner segments extend the whole depth 

 of the thallus, and the division into dorsal and ventral seg- 

 ments is secondary. The formation of the wings begins near 

 the apex and is the result of the growth of the marginal cells, 

 which project strongly and divide rapidly by vertical walls 

 only. The walls of the cells are thickened at the angles, and 

 the surface view is curiously like a cross-section of the collen- 

 chyma of many vascular plants. As in Anthoceros mucilage 

 slits are formed, sometimes on both surfaces of the thallus, and 

 through these the plant is infected with Nostoc, as in the other 

 Anthocerotes. In Dendroceros the Nostoc colonies are very 

 large and cause conspicuous swellings upon the thallus. All the 

 species of Dendroceros that have yet been examined are monoe- 

 cious. 



The antheridia of Dendroceros (Campbell (20)), which 

 are larger than those of the other two genera, are developed 

 singly in strict acropetal succession, forming a row on each side 

 of the midrib. The youngest ones occur very near the apex of 

 the shoot. The mother cell arises exactly as in Anthoceros and 

 Notothylas, and the periclinal division of the cell lying outside 

 it takes place very early, so that almost from the beginning 

 there are two layers of cells above the antheridial chamber. In 

 all the younger stages met with by the waiter, the antheridium 

 lay horizontally nearly parallel wnth the axis of the shoot, and 

 was attached to the back of the antheridal chamber, instead of 

 at its base, as in the other genera. (Fig. 78, D.) 



The first division in the antheridium is transverse, and sep- 

 arates the upper part from the stalk. The next divisions may 

 be alike in both of these cells, being vertical walls intersecting 

 so as to divide both cells longitudinally into four similar cells. 

 In the stalk, however, one of these divisions may be suppressed, 

 and in such cases, the stalk has but two rows of cells instead of 

 four. In the ripe antheridium the stalk becomes very long, and 

 is coiled up in the large antheridial chamber. 



