346 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA. 



arranged parenchyma, composed of branching rows of cells 

 (/>/) 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 <n-o ( u, mouth) forms a sort of shaft (g\ 

 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 " obtura- 

 tor 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 limita- 

 tion of the aperture. We shall hereafter find ( 245) that the 

 leaves of the higher plants contain intercellular spaces, which 

 also communicate 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. 



215. The basket-shaped " conceptacles" which are borne upon 

 the surface of the frond (Fig. 180, A), and which may often be 



FIG. 130. 



Gemmiparous conceptacles of MarcJiantia potymorpha: A, conceptacle fully expanded, rising 

 from the surface of the frond, a, a, and containing disks already detached ; B, first appearance of 

 conceptacle on the surface of the frond, showing the formation of its fringe by the splitting of the 

 cuticle. 



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 outgrowths. This fringe is at first formed by the split- 

 ting up of the epidermis, as seen at B, at the time when the con- 

 ceptacle and its contents are first making their way above the 

 surface. The little disks (sometimes termed "bulbels," from 

 their analogy to the bulbels or detached buds of Flowering 



