STRUCTURE AND DEVELOPMENT OF DENDROCEROS. 469 
as those produced in certain species of Anthoceros and Noto- 
thylas. In size they are intermediate between these, seldom 
exceeding one or two centimetres in length. Like all the other 
Anthocerotacez, the thallus always contains colonies of Nostoc, 
which are here very conspicuous and form large globular 
swellings upon the upper side of the thallus, close to the midrib. 
The thallus in all the described species of Dendroceros agrees 
in having a well-defined midrib and thin lateral lamina. In 
D. Breutelii the midrib shows no intercellular spaces, but small 
ones occur between the cells of the lamina. Certain species, 
however, like D. javanicus, Nees, have large lacune in the midrib, 
whose surface presents an areolated appearance like that of the 
Marchantiacee*. Similar lacune occur in the thallus of Noto- 
thylas orbicularis, Sulliv., and some species of Anthoceros. 
The apical growth of the thallus of D. Breutelii has been 
studied by Leitgeb t, and his account agrees in the main with 
my own, although there are one or two points of difference. A 
vertical longitudinal section (Pl. 21. fig. 1) presents the same 
appearances found in most fern-prothallia and in Pellia epiphylla, 
Corda. The large apical cell appears semicircular and extends 
the whole depth of the thallus, and the segments cut off from its 
inner face extend also completely from the dorsal to the ventral 
surface. Horizontal sections (figs. 2, 3) show at the apex one or 
two nearly oblong cells, and while it is probable that usually, 
at least, there is but one initial cell, it is possible that 
there may be more. In the form of the apical cell Dendroceros 
differs both from Notothylas and Anthoceros, where two sets of 
basal segments, alternately dorsal and ventral, are found, instead 
of the single one found in Dendroceros. 
Each primary basal segment of the apical cell in Dendroceros 
(fig. 1) is first divided into two equal cells by a median longi- 
tudinal wall, thus forming a dorsal and ventral semi-segment. 
Each of these is next divided by a vertical wall parallel to the 
base of the apical cell, so that the whole segment is now divided 
into four similar cells, two dorsal aud two ventral. Leitgeb's 
figure t does not show the formation of vertical walls until 
à much later period, the second walls in the segment being 
represented as horizontal. In all the preparations examined by 
the writer, the horizontal walls only arose after one set of 
* Leitgeb, Unters. üb. Lebermoose, Heft 5, p. 30. t L. e. p. 30. 
+ Leitgeb, J. c. pl. 2. fig. 1. 
