666 MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMS 



parenchyme, the projection of whose summits forms the raised 

 bands on the surface ; and above by an epiderm (6, b) formed of a 

 single layer of cells ; whilst its interior is occupied by a loosely 

 arranged parenchyme composed of branching rows of cells (f, 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 

 A j us t mentioned. If the vertical 



section should happen to traverse 

 one of the peculiar bodies which 

 occupy the centres of the divi- 

 sions, it will bring into view a 

 structure of remarkable com- 

 plexity. Each of these stomates 

 (as they are termed, from the 

 (ireek crrof^a, mouth) forms a sort 

 of shaft (r/), composed of four or 

 five rings (like the ' courses ' of 

 bricks in a chimney) placed one 

 upon the other (A), every ring- 

 being made up of four or five 

 cells; and the lowest of these 

 rings (/) appears to regulate the 

 aperture by the contraction or 

 expansion of the cells which 

 compose it, and is hence termed 

 the ' obturator-ring.' In this 

 manner each of the air-chambers 

 of the frond is brought into coin- 



FIG. 504. Structure of frond of Marchan- 

 tia polymorpTia : A, portion seen from 

 ;il.ove; a a, lozenge-shaped divisions; 

 0.0, stomates m the centre or the lozenges; 

 c, c, greenish bands separating the 

 lozenges. B, vertical section of the frond, atmosphere, the degree of 



munication with the 



showing a, a, the dense layer of cellular 

 tissue forming the floor or the air- 

 " 



external 

 that 



commimicat j oll being 



< 



regulated 



- . 



chamber, d, ,7, "the epidermal layer, I, b, by the limitation of the aperture. 

 forming its roof ; r, c, its walls;/,/, loose 

 cells in its interior ;,/,tomate divided per- 

 pendicularly ; fe, rmgs of cells forming its 

 wall ;/, cells, forming the obturator-ring, 



shall hereafter find that the 

 leaves of the higher plants con- 

 tain intercellular spaces, which 

 also communicate with the ex- 

 terior by stomates, but that the structure of these organs is far less 

 complex in them than in this humble liverwort. 



The frond of Marchantia usually bears upon its surface, as shown 

 in fig. 503, a number of little open basket-shaped yemmiparous ant 

 ceptacles (fig. 505), which may often be found in all stages of develop- 

 ment, and are structures of singular beauty. They contain when 

 mature a number of little green round or oblong discoidal (/emmce, 

 each composed of two or more layers of cells ; and their wall is sur- 

 mounted by a glistening fringe of teeth.' whose edges are themselves 

 regularly fringed with minute outgrowths. This fringe is at first 

 formed by the splitting up of the epiderm. as seen at I!, at the 

 time when the conceptaele and its contents are first making their 

 wav above the surface. The little genuine are at first evolved as 

 single globular cells, supported upon other cells which form 

 footstalks; these sinyle cells, undergoing binary subdivision. 



their 

 evolve 



