242 DupLeR: AIR CHAMBERS OF REBOULIA 
of the air chambers. In this connection two points of view have 
been emphasized, viz., that of Leitgeb (12, 13, 14), who regarded 
them as formed by a dorsal upgrowth arising from superficial 
cells, and that of Barnes and Land (1), who pointed out the internal 
schizogenous origin of the airchambers. A summary of the earlier 
literature dealing with this problem, dating back to Hofmeister 
(11), is to be found in the paper by Barnes and Land; while the 
later literature has been reviewed by Evans (7). In the present 
paper reference is made to the recent literature only when it 
bears somewhat directly on Reboulia itself or its close allies. 
Leitgeb’s interpretation of the structure and partitioning of 
the air chambers of Reboulia, as noted above, has been generally 
accepted by such writers as Cavers (4, 5), Campbell (3), and 
Goebel (8). Cavers notes that near the apex there is but a 
single layer of chambers, each with a simple pore, but that the 
chambers become partitioned as they develop. Campbell holds 
for Reboulia and Fimbriaria (F. californica is especially described) 
that there is a more or less complete division of the primary 
chambers by the formation of diaphragms. Barnes and Land (1) 
state that in Plagiochasma it appears probable that the partitioning 
of the chambers occurs as described by Leitgeb but that “the 
formation of the aerating tissue is mainly due to splitting and 
growth.” From her study of Plagiochasma (Aytonia) Miss Starr 
(16) claims that Leitgeb’s partitioning plates are not outgrowths 
but arise by “stretching and tearing of tissues between neighboring 
chambers . . . the tearing being due to the differences in tension 
between the upper and lower parts of the thallus. This leaves pro- 
jecting plates of cells, appearing as filaments in section, which Leit- 
geb and Campbell interpreted as new growth dividing the original 
chambers. Perhaps these plates add to their length by further 
growth.” Evans (7) has made a very careful study of the air 
chambers in Grimaldia fragrans, and his results are of importance 
in a comparison with Reboulia. He finds that the primary cham- 
bers of the dorsal region “are subdivided by an irregular system of 
more or less vertical, united cell plates, enclosing narrow spaces, 
so that the boundaries of the chambers are difficult to distinguish.”’ 
He finds that these plates may end freely below the epidermis or 
extend to the epidermis but that “it isdoubtful . . . if the connec- 
