246 Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 
In Fic. 7, which represents the apical region of another thallus, 
a somewhat different condition is revealed. In this case the 
first indication of an air chamber appears between the third and 
fourth cells and is likewise in the form of a split, but this time the 
split evidently began on the outside and extended inward. Al- 
though the chamber is thus superficial in origin, there is no evidence 
that a surface area has had its upward growth arrested, as Leit- 
geb’s explanation demands. The split clearly extends inward 
from the original surface. The chamber between the fourth and 
fifth cells is considerably deeper and broader, and it is clear that 
its increase in size has involved further schizogenous processes. 
The next chamber shown gives evidence of a further horizontal 
extension. 
It would appear from these two figures that the air chambers 
in Grimaldia fragrans owe their origin to a splitting of cell walls, 
but that the place where the split first makes its appearance is not 
always the same. It may be below the surface and extend out- 
ward, in which case it agrees fully with the explanation advanced 
by Barnes and Land; it may be at the surface and extend inward, 
thus agreeing with Deutsch’s account of Targionia hypophylla. 
In the writer’s opinion the figures published by Miss Hirsh and 
Miss Black might be interpreted in the same way as FIG. 7, so 
that there still seems to be no conclusive evidence that Leitgeb’s © 
explanation ever applies. 
Fics. 8-10 yield further evidence as to the origin of the cham- 
bers; they were all drawn from a single section, cut at right 
angles to the long axis of the thallus, and show for the most 
part superficial cells. In Fic. 8 the apical cell appears in the form 
of a rectangle. Directly above it an air chamber reaching the 
surface is shown between the fourth and fifth cells, corresponding 
apparently with the chamber between the fourth and fifth cells 
of Fic. 7. The schizogenous origin of this chamber seems clear, 
but there is nothing to show whether the split began at or below 
the surface. Between the third and fourth cells no signs of a 
chamber can be discerned, although a superficial split may be 
present like the one shown in Fic. 7. The figure at any rate gives 
no evidence of a split beginning below the surface. 
Fics. 9 and 10 are much more conclusive. They represent a 
