326 MOSS URNS. PART 11. 



ally produces four unripe spores, which get an exterior 

 coat when fertilised, and then it is that the stalk 

 lengthens, and the flask-shaped archegonium is torn 

 across. 



The urns are closed by a lid or operculum of a flat, 

 convex, or pointed form, which falls off" when the spores 

 are ripe to give them egress. The mouth of the urn 

 in most of the mosses is surrounded by a deciduous 

 annulus of two or three rows of elastic cells, which are 

 supposed to aid in scattering the spores, for the mosses 

 have no elaters. Although the separation of the lid 

 may at once expose the spores, they may be covered 

 with a membrane entire or toothed at the circumfer- 

 ence, or there may be one or two rows of teeth sur- 

 rounding the mouth of the urn like a fringe; these 

 teeth form the peristome, and their number is always 

 a multiple of 4, varying from 4 to 64 (see fig. 47 p). 

 Sometimes they are divided half way down, sometimes 

 they are prolonged into straight twisted hairs. The 

 teeth arise from the thickening of the walls of two con- 

 tiguous cells; when there are two rows of teeth, the 

 outer row frequently arises from the layer of cells which 

 line the outer wall of the urn, the inner row from the 

 outermost layer of the spore sac ; sometimes, when the 

 peristome is double, three strata of cells are requisite 

 to form the teeth. The urns of the Encalypta vulgaris 

 are represented at fig. 47 B ; one is covered with the 

 hood or calyptra, while from the other the lid has fallen 

 off, showing the mouth of the urn with its toothed 

 peristome. 



When a spore begins to grow, its outer coat is ruptured, 

 its innermost coats protrude and form a projecting ex- 

 tremity, which becomes developed into a confervoid pro- 

 embryo, analogous to the mycelium of fungi, but is dis- 

 tinguished by the chlorophyll contained in its cells. 

 Many spores may concur or not in its formation ; but 



