666 MICKOSCOPIC STKUCTURE OF HIGHER CRYPTOGAMS 



parenchyma, the projection of whose summits forms the raised 

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

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

 arranged parenchyme 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 

 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 

 Greek oro/io, mouth) forms a sort 

 of shaft (y), 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 (i) appears to regulate the 

 aperture by the contraction or 

 expansion of the cells which 

 compose it, and is hence termed 

 FIG. 504.-StructureoffrondofMarc^a- the ' obturator-ring/ In this 

 tia polymorpha : A, portion seen from manner each of the air-chambers 

 above; a a, lozenge-shaped divisions; o f the frond is brought into COin- 

 b,b, stomates in the centre of the lozenges; . <- , 



c, c, greenish bands separating the munication With the external 

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



showing -a, a, the .dense layer of cellular commun i cat i O n being regulated 



tissue forming the floor of the air- . ...... 



chamber, d, d, the epidermal layer, 6, 6, by the limitation of the aperture. 



forming its roof ; c, c, its walls ; /,/, loose We shall hereafter find that the 



cells .in its interior; g, stomate divided per- j f tl higher plants CO11- 



pendicularly; Brings of cells forming its . . 



wall ; i, cells, forming the obturator-ring, 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 gemmiparous con- 

 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 gewimt'. 

 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 B, at the 

 time when the conceptacle and its contents are first making their 

 way above the surface. The little gemmae are at first evolved as 

 single globular cells, supported upon other cells which form their 

 footstalks ; these single cells, undergoing binary subdivision, evolve 



