470 PROF. D. H. CAMPBELL ON THE 
vertical ones had been formed. As soon as the horizontal walls 
are formed in the dorsal and ventral cells the midrib becomes 
four cells thick, and later horizontal walls make it much thicker 
farther back from the apex. As the alternation of vertical and 
horizontal walls is quite regular for some time, the limits of the 
original segments can be traced for a considerable distance back 
from the apex. Besides the basal segments, which contribute 
mainly to the formation of the midrib, there are also formed 
lateral segments which remain undivided by horizontal walls, and 
give rise to the thin lamina. 
The formation of the “stomata” or mucilage-slits upon the 
thallus was not studied in detail, as Leitgeb has given a full and 
accurate account of these structures, which agree in all par- 
ticulars with the similar ones in Anthoceros. As in Anthoceros, 
these are always associated with the formation of the conspicuous 
Nostoc-colonies, the filaments entering the thallus through the 
mucilage-slits. 
2) 
The Sexual Organs. 
All the species of Dendroceros examined are moncecious, 
and there is no evident regularity in the occurrence of antheridia 
and archegonia, except that as a rule several of one or the other 
are formed in succession. Asin all the Anthocerotacee, they are 
sunk in the thallus and are very inconspicuous, except 1n the 
case of the older antheridia, which in Dendroceros are very much 
larger than in either Anthoceros or Notothylas. 
Leitgeb gives a brief account of the archegonium, but there 
are several points worthy of note which he seems to have over- 
looked. As the young archegonium is completely immersed 10 
the thallus, and the mother-cell hardly distinguishable from the 
surrounding tissue, it is not possible to assert positively its om 
relation to the segment of the apical cell in which it 18 forme . 
The walls by which it is cut out, seen in transverse sect 
intersect so as to enclose a triangular cell, as was shown Jy 
Leitgeb, and in this respect it agrees with the other Anthoo® 
rotaces. This cell then by transverse divisions (fig. 5) gives T! 
to the axial row of three cells, found in the young archegomum™: 
The lower cell, by a subsequent division, gives rise to the e 
cell and ventral canal-cell ; the middle one, by a series of mis , 
verse walls, produces the row of four or five neck aa ae 
while the upper one, by two intersecting vertical walls but 
the four cover-cells, or, by the suppression of one of the walls; 
