Evans: AIR CHAMBERS OF GRIMALDIA FRAGRANS Paes 
grow upward from the floors and lateral walls of the chambers. 
A spongy tissue is thus formed in which narrow air spaces run, 
scarcely broader than the thickness of the lamellae, and the original 
partitions of the chambers soon become unrecognizable. He 
admits that in section the plates of cells one cell thick look like 
filaments and that marginal cells of the plates sometimes project 
as teeth, but he maintains that actual filaments are never present 
and that this fact is at once made evident by sections of the green 
tissue cut parallel with the surface of the thallus. Massalongo 
(5, p. 730), on the other hand, agrees with Stephani and states that 
the chambers are filled with vertical uniseriate filaments, some of 
Fic. 1. Transverse section through epidermis and green tissue, X 270 A 
air chambers; e-g, apparent filaments; h, plate-like outgrowth; 7, k, 1, boundaries 
between chambers. 
them reaching the epidermis. His figures not only show filaments 
clearly but indicate that the boundaries of the chambers are 
distinct, in this respect also differing from Schiffner’s account. 
The green tissue of G. fragrans is so compact that it is difficult 
to make out its true structure from ordinary hand sections. Even 
microtome sections are not always easy to interpret, but they give 
a much clearer idea of the complex arrangement of the cells and 
of the intricate system of aérating chambers and help to explain 
some of the conflicting statements in the published descriptions. 
In a transverse section, such as the one shown in Fie. 1, the cham- 
