70 COMPOUND ORGANS OF PLANTS. 



swell and the sporangia to form. By the expansion of the 

 sporangium, the calyptra which incloses it is separated, or 

 rather torn from its base, and carried upwards on the apex of 

 the sporangium. If, when this happens, the calyptra is torn 

 away equally on all sides from the base of the sporangium, 

 so as to hang over it vertically, the calyptra is said to be 

 mitriform, or mitre-shaped. If, on the contrary, the rupture 

 takes place unequally, by the adhesion of part of the mem- 

 branaceous matter of the calyptra to the base of the sporan- 

 gium, the sporangium, in swelling, necessarily splits up the 

 calyptra on one side, so that when the adhesion is overcome 

 the calyptra is ultimately carried up, and has an angular in- 

 clination to the surface of the sporangium; in, this case, the 

 calyptra is said to be cuculliform (cucuUum, a hood). When 

 the calyptra has fallen, the sporangium is seen to be inclosed 

 by an operculum or lid, which assumes different shapes in 

 different species, being convex, conical, or rostrate (rostrum, 

 a beak). As fructification 'advances, the operculum or lid 

 falls, and the peristome {itipi around, ato/ia mouth) or mouth 

 of the sporangium is revealed, which, in some species, presents 

 to the eye the appearance of a beautiful fringe, the organiza- 

 tion of which can only be distinguished by the microscope. 



91. As an illustration of the parts already described. Fig. 

 29 is given, which is taken from Dr. Gray's Botanical Text- 

 Book. 



92. When the peristome of different species of mosses is 

 examined, it is found to consist in some of an inner and 

 outer peristome, which is, in fact, a peculiar organic modifi- 

 cation of the inner and outer membrane of the sporangium. 



