Evans: Air chambers of Grimaldia fragrans 237 



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 



Fig. I. Transverse section through epidermis and green tissue, X 270. a-d, 

 air chambers; e-g, apparent filaments; h, plate-Hke outgrowth; i. k, I, 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 difiicult 

 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 aerating chambers and help to explain 

 some of the conflicting statements in the published descriptions. 

 In a transverse section, such as the one shown in FiG. i, the cham- 



