The air chambers of Grimaldia fragrans * 
ALEXANDER W. EVANS 
(WITH FOURTEEN TEXT FIGURES) 
INTRODUCTION 
In most of the Marchantiales the thallus shows a layer of 
green tissue with air spaces or chambers below the dorsal epidermis. 
These chambers exhibit many differences when the group as a 
whole is considered, but it is possible to refer the majority to three 
distinct types. To these the names of the representative genera 
Riccia, Reboulia and Marchantia may be applied. 
In the Riccia type the chambers occupy a single layer and are 
in the form of canals with their long axes approximately vertical; 
the canals are usually narrow and bounded by only four rows of 
cells, but in certain cases they are broader and bounded by a 
greater number of cells. In the Reboulia type the chambers are 
in two or more layers (at least in the median portion of the thallus) 
and are in the form of irregular polyhedrons, often tending to be 
isodiametric; this type is sometimes complicated by cellular out- 
growths into the chambers. In the Marchantia type the chambers 
are again in a single layer (as in the Riccia type) but are in the 
form of more or less flattened polygonal prisms with their longer 
dimensions approximately horizontal; they are further distin- 
guished by the presence of numerous simple or branched green 
filaments, extending from the floors of the chambers nearly or 
quite to the epidermis. In all three types the chambers communi- 
cate with the outside air by means of openings in the epidermis. 
In the Riccia type these may be nothing more than continuations 
of the canalicular chambers, but in the two other types the open- 
ings are usually surrounded by specialized epidermal cells and 
form the characteristic air pores or epidermal pores of the group. 
Among North American genera the Riccia type is restricted to 
Riccia and Oxymitra; the Reboulia type is found in Ricciella, 
* Contribution from the Osborn Botanical Laboratory. 
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