Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS 247 
portion of the thallus to the right of the apical cell and derived 
from lateral segments. In drawing Fic. 9 the microscope was 
focused on the surface of the cells in a circumscribed area; in 
drawing Fic. 10 it was focused a little below the surface of the 
same area. FIG. 9 shows a series of cells in close union and two 
air chambers which have reached the surface; F1c. 10 shows the 
same two chambers and six additional ones. The latter clearly 
represent schizogenous spaces below the surface and demonstrate 
an origin like that of the youngest chamber in Fic. 6. 
Fic, 8. Transverse section through a growing point, xX 500. x, apical cell. 
Fic. 9. Superficial cells to the right of the apical cell shown in Fic. 8, X 500. 
Fic. 10. The same region as that shown in Fic. 9, but at a slightly lower focus, 
more very young dorsal pores bene anes x bh 
FI Slightly older d h in Fic. 10, the section 
G. II. oiightly older 
parallel with the surface, X 500. 
Section just below the one shown in FiG. 11, the numerous intercellular 
00. 
Fic. 12 
spaces being the beginnings of more deeply situated chambers, 
The rudimentary chambers shown in FiGs. 6-10 represent the 
beginnings of the complex dorsal chambers shown in Fics. 1-4. 
The later stages in the development of these chambers and the 
origin and development of the more deeply situated chambers are 
exceedingly difficult to follow. For a while the dorsal chambers 
are distinct enough in sections cut immediately below the epider- 
mis. Such a section is shown in Fic. 11, where two complete 
chambers and parts of six others are represented. The increase 
