Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 249 
vertical, the growth in the latter direction being often equalled 
by the upward growth (accompanied by cell division) of the cells 
forming the floors of the chambers; these in turn remain more or 
less united with one another and with the cells of the partitions 
and in this way form the system of united cell-plates in the dorsal 
chambers. At a later stage the margins of some of the plates 
which end freely in the chambers give rise to teeth as shown in 
FiG. 2. 
It is difficult to secure direct evidence from the vegetative 
thallus that the partitions form surface-outgrowths. Fic. 14, 
however, which is drawn from a sec- 
tion of the young female receptacle, 
shows that such outgrowths are pos- 
sible. The section was cut parallel 
with the upper surface of the recep- 
- tacle, and the figure shows two com- 
plete chambers and parts of eight 
others; two of the latter contain sec- 
tions of the tubular epidermal pores 
which hang down from the roofs of 
the chambers. The partitions are one 
cell thick but give the impression of 
being thicker when cut obliquely. 
The outgrowths originate as projec- Section parallel with 
; ‘ the surface of a young female re- 
tions of cells which become cut off by sindbis Yaak tebits the eplaeriaia 
walls and then continue their growth x 270. 
and cell-divisions. In the vegetative 
thallus such outgrowths evidently play a very minor part in the 
development of the green tissue. 
The chambers below the dorsal layer make their appearance 
very early, as seen in Fics. 12 and 13, although they always appear 
later than the dorsal chambers. As the thallus becomes differen- 
tiated, these chambers increase rapidly in size through the growth 
of the bounding cells, but the appearance of new chambers, except 
in the apical region, has not been demonstrated and seems im- 
probable. If schizogenous processes play a part in the enlarge- 
ment of these chambers, it is only to a very limited extent. 
The green tissue in the thallus of Plagiochasma bears a strong 
