LIVERWORTS I STRUCTURE OF MARCHAXTIA. 367 



corresponds with an air-chamber in its interior, which is bounded 

 below by a floor (a, a) of closely-set cells (from whose under 

 surface the radical filaments arise); at the sides by walls (c, c) of 

 similar solid parenchyma, the projection of whose summits forms 

 the raised bands on the surface; and above by a cuticle (b, b) 

 formed of a single layer of cells ; whilst its interior is occupied 

 by a very loosely arranged parenchyma, composed of branching 

 rows of cells (/, f) that seem to spring from the floor, — these cells 

 being what are seen from above, when the observer looks down 

 through the central aperture just mentioned. If the vertical 

 section should happen to traverse one of the peculiar bodies which 

 occupies the centres of the divisions, it will bring into view a 

 structure of remarkable complexity. Each of these Stomata (as 

 they are termed, from the Greek ero^a, mouth) forms a sort of 

 shaft ((/), composed of four or five rings (like the 'courses' of 

 bricks in a chimney) placed one upon the other (h), every ring 

 being made up of four or five cells ; and the lowest of these rings (i) 

 appears to regulate the aperture, by the contraction or expansion 

 of the cells which compose it, and it is hence termed the ' obtu- 

 rator ring. ' In this manner each of the air-chambers of the frond 

 is brought into communication with the external atmosphere, the 

 degree of that communication being regulated by the limitation of 

 the aperture. "We shall hereafter find (§ 314) that the leaves of 

 the higher Plants contain intercellular spaces, which also com- 

 municate with the exterior by Stomata ; but that the structure of 

 these organs is far less complex in them than it is in this humble 

 Liverwort. 



273. The basket-shaped Conceptades which are borne upon the 

 surface of the frond (Fig. 178, a), and which may often be found 

 in all stages of development, are structures of singular beauty. 

 They contain, when mature, a number of little green round or 

 oblong disks, each composed of two or more layers of cells ; and 

 their wall is surmounted by a glistening fringe of 'teeth,' whose 

 edges are themselves regularly fringed with minute out-growths. 

 This fringe is at first formed by the splitting-up of the epidermis, 

 as seen at b, at the time when the conceptacle and its contents are 

 first making their way above the surface. The little disks (some- 

 times termed 'Bulbels,' from their analogy to the bulbels or 

 detached buds of Flowering Plants) are at first evolved as single 

 globular cells, supported upon other cells which form their foot- 

 stalks ; these single cells gradually undergo multiplication by 

 duplicative subdivision, until they evolve themselves into the disks ; 

 and these disks, when mature, spontaneously detach themselves 

 from their footstalks, and lie free within the cavity of the concep- 

 tacle. Most commonly they are at last washed out by rain, and 

 are thus carried to different parts of the neighbouring soil, on 

 which they grow very rapidly when well supplied with moisture ; 

 sometimes, however, they may be found growing whilst still con- 



