MICROSCOPIC STRUCTURE OF HIGHER CRYPTOGAMIA. 337 



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, ifc will bring into view a structure of remarkable complexity. 

 Each of these stomata (as they are termed, from the Greek 6rofA.a, 

 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 (7^), 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 the 'obturator-ring.' In 

 this manner each of the air-chambers of the frond is brought into com- 

 munication with the external atmosphere, the degree of that communica- 

 tion being regulated by the limitation of the aperture. We shall here- 

 after find ( 383) that the leaves of the higher Plants contain inter- 

 cellular spaces, which also communicate with the exterior by stomata; 

 but that the structure of these organs is far less complex in them, than 

 in this humble Liverwort. 



333. The frond of Marchantia usually bears upon its surface, as 

 shown in Fig. 214, a number of little open basket-shaped gemmiparous 

 conceptacles (Fig. #16), which may often be found in all stages of de- 

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

 mature, a number of little green round or oblong discoidal gemmce, 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 which correspond with the gonidia of Lichens ( 325), are at first 

 evolved as single globular cells, supported upon other cells which form 

 their footstalks; these single cells, undergoing duplicative subdivision, 

 evolve themselves into the disks; and these disks, when mature, sponta- 

 neously detach themselves from their footstalks, and lie free within the 

 cavity of the conceptacle. Most commonly they are at last washed out 

 by rain, and are thus carried to different parts of the neighboring soil, 

 on which they grow very rapidly when well supplied with moisture; some- 

 times, however, they may be found growing whilst still contained within 

 the conceptacles, forming natural grafts (so to speak) upon the stock 

 from which they have been developed and detached; and many of the ir- 

 regular lobes which the frond of the Marchantia puts forth, seem to have 

 this origin. The very curious observation was long ago made by Mirbel, 

 who carefully watched the development of these gemmcB, that stomata are 

 formed on the side which happens to be exposed to the light, and that 

 root-fibres are put forth from the lower side; it being apparently a matter 

 of indifference which side of the little disk is at first turned upwards, 

 since each has the power of developing either stomata or root-fibres 

 according to the influence it receives. After the tendency to the forma- 

 tion of these organs has once been given, however, by the sufficiently 

 prolonged influence of light upon one side and of darkness and moisture 

 on the other, any attempt to alter it is found to be vain; for if the sur- 

 faces of the young fronds be then inverted, a twisting growth soon re- 

 stores them to their original aspect. 



334. When the Marchantia vegetates in damp shady situations which 

 are favorable to the nutritive processes, it does not readily produce the 



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