370 



PAET III. THE CLASSIFICATION OF PLANTS. 



species of Pottia and Encalypta, Seligeria Doniana, Orthotrichum gymnostomum, 

 etc.) belonging to genera in which a peristome is usually present. 



As the capsule matures, the cells (except the spores) lose their cell-contents ; 

 and those whose walls have not become thickened and cuticularised, dry up and 

 shrink, the shrinkage being necessarily accompanied by the tearing of the thin 

 walls in various parts. The persistent cuticularised walls are highly hygro- 

 scopic, and it is in consequence of the tensions set up by the unequal stretching 

 and contraction of these walls, due to variations in their moisture, that the split- 

 ting off of the operculum is effected. 



tt. 



FIG. 253. Sporogoninm of Funaria hygrometrica. A, s setfi, ; b capsule ; c calyptra ( x S). 

 S Section of a half-developed capsule (x 10): c columella; s archesporium ; I air-cavity; 

 d sub-opercular tissue ; p peristome. C Apical portion of the same capsule ( x 40) ; <J oper- 

 culum; id sub-opercular tissue; ap outer peristome; ip inner peristome; r ring; I air- 

 cpace; c columella; s spore-sac. 



The Stegocarpae are classified as follows : 



Sub-tribe ACROCARPM : archegonia terminal on the main shoots ; but the 

 sporogonia are sometimes apparently lateral in consequence of the growth of 

 lateral branches (innovations) which force the apex of the main shoot to the 

 side. The following are the principal families and genera : 

 Fam. 1. Weisiacea : Bymenostomum, Gymnostomum, Weisia. 



2. Dicranacece : Dicranum, Dicranella. 



,, 3. Leucobryacece : Leucobryum. 



,, 4. Fissidentacea : Fissidens. 



5. SeligeriacecB : Seligeria small mosses growing only on rocks. 



6. Pottiacece : Pottia, Tortula, Barbula, Trichostomum, Ceratodon. 



7. Grimmiaceee : Grimmia, Racomitrium, Hedwigium. 



8. Orthotrichacea : Orthotrichum, Zygodon. 



9. Encalyptacea : Encalypta. 



,, 10. Georgiacea: Georgia (Tetraphis), Tetrodontium. 



11. Schistostegacea : Schistostega. 



,, 12. Splachnacece : Dissodon, Tayloria, Splachnum. 



,, 13. Funariacece : Physcomitrium, Funaria. 



,, 14. Mniacea : Mnium, Meesia, Aulacomniuna. 



,, 15. Bryacece : Bryum, Webera. 



16. Polytrichacece : Atrichum, Polytrichum, Pogonatum. 

 17. Buxbaumiacece : Buxbaumia. 



