12 



. VORkSlilRl: NAtiJKALISTS* UXiON". 



outer la)^er is composed of two rows of cells jointed together 

 transversely, firm and often richly coloured, brown, yellow^, red, 



F 



etc., but on the inner surface of the tooth we Hnd only one layer 

 of cells, which are thin and vesicular, and their adjacent walls 

 are thickened into transverse plates or lamella. 



See now how this difference in structure acts; the thin 

 internal cells absorb water quickly, and consequently swell up 

 and shorten the inner face of the tooth, to which the hard outer 

 cells can only yield at the transverse joints, and they thus bend 

 inward and shut up the mouth of the capsule, and this trivial 

 thing, as we may consider it, puts in action the teeth of thousands 

 of moss capsules every rainy day, and forms an important phase 

 in their life-history. 



At base the peristome cells are united to the innermost 

 layer of the capsular w^all ; but this is not all, for in these higher 

 mosses, Bryiun^ Mfiiia/i^ HypJiuni^ etc., within the peristome is a 

 series of appendages, the inner peristome or endostome, a 

 delicate membrane, continuous with the outer layer of the spore- 

 sac, and prolonged into sixteen processes, alternating with the 

 outer teeth, and commonly perforated in the middle line, also 

 having one to four slender cilia between each pair of processes. 



In Buxhaumia and Wchcra the endostome forms a plicate 

 tube, in Cindidluin the processes are united at top into a beauti- 

 ful dome, and in Font'uialis they form a crimson ladder by means 

 of transverse cross-bars. Of course when the lid comes away the 

 spore-sac is ru])tured and the spores are scattered ; this must be 

 effected by the wind when the peristome is ill-developed, as w^e 

 may notice that in most of these the capsule is erect^ but in 



Bot. Trans, Y.N^U, ISU^Upub. ISOtJ). 





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