The development of air chambers in the Ricciaceae 
PAULINE E, HirsH 
The thallus in the family Ricciaceae is characterized by the 
presence of clearly defined air spaces, varying in different species 
in size and shape. On the basis of the structure of the tissues 
and enclosed air chambers a subdivision of the old genus Riccia 
into smaller genera is made by some writers. For example, 
Evans and Nichols in their “‘ Bryophytes of Connecticut’’ have 
placed in the genus Azccia those species with air spaces in the 
form of narrow canals lying between rows of cells at right angles 
to the upper surface of the thallus. Species with the green tissue 
arranged in layers one cell thick, separating irregular air spaces 
from one another, they placed in the genera Riccie/la and Riccio- 
carpus, the latter characterized by an epidermis with pores, the 
former by an epidermis without pores, though sometimes becoming 
ruptured irregularly with age. 
In the Botanical Gazette for September, 1907, Barnes and Land 
published a paper dealing with the origin of air chambers in the 
Marchantiales. They studied representatives of as many groups as 
they could obtain, and described results so uniform as to make it, 
in their opinion, a matter of doubt whether any other mode of 
origin exists than that found in every plant investigated. They 
concluded that the ‘‘ air chambers of Marchantiales arise invariably 
by the splitting of internal cell walls, usually at the junction of the 
outermost and first internal layer of cells.’* In the Ricciaceae 
they examined only Riccia fluitans and R. natans. They stated 
that in these species “the origin of the air chambers is exactly 
alike, though the later course of development seems to be differ- 
ent. The origin of both is certainly by internal cleavage, and it 
is quite evident that the air chamber is wholly unrelated to the 
sex-organ pit.” 
At the time that the present study was undertaken, the only 
fresh material available was ‘‘ Riccia /utescens,’ the terrestrial form 
* Barnes and Land. Bot. Gaz. 44: 213. 1907. 
7 Barnes and Land. JZ. ¢. 205. 
