180 MORPHOLOGY. 



a. The lower cellular tissue is very much elongated, and thus 

 forms a filiform support for the rest; sometimes it becomes 

 blended with the middle one by a gradual swelling, forming the neck 

 or collum, or it forms a more sharply defined thickening of a differ- 

 ent form, the apophysis, especially marked in Splachnum. 



b. The middle portion forms an urn-shaped, almost cylindrical, 

 seldom obtusely angular, or plano-convex organ, and becomes de- 

 veloped into different layers: (1.) to a central, either cylindrical or 

 more spherical, cellular mass, the columella ; (2.) to the coating of the 

 theea ; and (3.) to a delicate cellular tissue lying between the other 

 two, the cells of which, developing as sporangia into four (?) spores, 

 become dissolved and absorbed, so that the spores are left free. Each 

 spore-cell secretes within the sporangium a peculiar membrane, 

 which is either smooth, or covered with larger or smaller warts and 

 areolas. The wall of the theca itself consists, externally, of an inte- 

 gument in which several layers of a thin-walled, close cellular 

 tissue are formed the outer membrane (membrana. external), inter- 

 nally of several layers of close cellular tissue the inner membrane 

 (membrana inferno), surrounding the spores. Between these two 

 lies a layer of extremely porous, often almost filamentous, loose 

 cellular tissue, which is sometimes absorbed by the time the sporo- 

 carp is ripe. 



c. The upper portion of the cellular tissue of the nucleus is de- 

 veloped into such heterogeneous cellular structures, that it sepa- 

 rates, in drying, into many parts, by the unequal contraction, and 

 the rending of homogeneous from heterogeneous rows of cells, partly 

 from within outward, and partly in a lateral direction. A layer 

 of more solid cellular tissue, in the form of a cover (operculum), 

 either flattish, convex, pointed or peaked, separates on the exte- 

 rior from the upper portion of the nucleus, and, at the same time, 

 from the theca. In most Mosses an annular layer of three or four 

 rows of cells (annulus) occurs, obliquely interposed from below 

 and from without, upwards and inwards, between the theca and 

 the operculum. In the interior, the columella is naturally conti- 

 nued from the theca into the point of the operculum. Its ex- 

 tremity appears sometimes on the falling off of the operculum, as a 

 disc or membrane, closing the whole aperture of the theca (stoma). 

 The remaining cellular tissue, between the end of the columella and 

 the operculum, is developed into a highly hygroscopic tissue, which 

 separates in various ways, either only laterally, into from four to 

 sixty-four acutely pointed lobes, teeth (denies) ; or, at the same 

 time, from within outward, so that two rows of such lobules ap- 

 pear, the innermost of which, where broader and alternating with the 

 teeth, are called processes, and the narrower ones occurring be- 

 tween these processes, the cilia. The inner layer occasionally appears 

 to cohere, entirely or partially, into a membrane ; but the external 

 one more rarely. The cells of the external lobules, almost all 

 manifest the peculiarity that their lower and upper walls become so 



