INTRODUCTION TO CETPTOGAMIC BOTANY. , 489 



sporangium, but the whole aperture is closed by a diaphragm, 

 from which an orbicular central portion at length separates 

 with the columella, which contracts within the sporangium. 

 LyelUa is a Nepalese, Bawsonia an Australian genus, extend- 

 ing to New Zealand. In D. superha no part of the peristome 

 adheres to the columella.* Polytrichwm is an enormous genus, 

 and is found everywhere. P. dendroides is a foot or more 

 high, and has a wide range in the southern hemisphere ; this, 

 however, is equalled if not exceeded in size by P. giga/nteum; 

 P. tortile extends from Surinam to New Zealand, while P. 

 juniperinum is almost cosmopolitan ; P. aloides occurs in 

 several places in India ; P. ciliatv/m, as the name implies, 

 has the leaves beautifully ciliated ; P. giganteum is one of the 

 largest of mosses. It has been stated that the stem of some of 

 the large Polytricha shows concentric rings of growth, but I 

 have been unable to detect such a structure. The leaves of 

 Polytricha, except in a few instances, are very rigid, and their 

 nerve often exhibits on its surface numerous lamelliform folds. 



Polytrichum dendroides. 



a. Horizontal section, slightly magnified. 



h. Vertical section of light coloured cells containing starch grains, 

 highly magnified. 



c. Ditto of dark external cells showing scalariform markings on the 

 walls, too strongly expressed in the figure. 



d. Horizontal section of one of the same cells. 



19. Leptostomei, Mont 



Sporangium ascending ; mouth contracted ; peristome mem- 

 branaceous, annuliform, erect ; leaves oblong, terminated by 

 a hair. 



* The teeth of -Po/yiric/iMTO consist of many threads soldered together. 

 Dawsonia exhibits these threads in a state of solution. 



