Evans: Air chambers of Grimaldia fragrans 239 



rise to outgrowths, as Schiffner suggests may be the case. The 

 original boundaries of the dorsal air chambers are not absolutely 

 unrecognizable, but they are by no means as distinct as Massa- 

 longo's figure represents them. In Fig. i the boundaries of the 

 chamber with the air-pore are shown at i and k, while another 

 boundary is situated at /. 



The longitudinal section drawn (FiG. 2) brings out the fact 

 that many of the air chambers are more or less elongated. This 

 is strikingly true of those most deeply situated but is also well 



Fig. 2. Longitudinal section through epidermis and green tissue, X 270. 



shown by the chamber with the air-pore, although the actual 

 boundaries of this chamber are not definitely indicated. It will 

 be noted that the upper margin of the cell plate represented, which 

 extends almost longitudinally beneath the pore, is distinctly 

 dentate, some of the teeth being over a cell in length. This 

 accords, on the whole, with Schiffner's statement that the marginal 

 cells of the plates may project as teeth. Although some of the 

 teeth shown are more than projecting cells, it would be a stretch 

 of the term to describe them as filaments. The figure, therefore, 

 presents no evidence of the occurrence of true filaments. Other 

 sections, however, show apparent filaments, similar to those 

 represented in FiG. i. 



According to Schiffner, a section through the green tissue paral- 

 lel with the surface of the thallus will at once show that the cham- 

 bers are destitute of free filaments. Fig. 3 shows a part of such a 



