54 MOSSES AND LIVERWORTS 



limestone nature. Pig. 2 of Plate IV.b is another 

 illustration of a ribbed capsule. In the Hair-moss 

 (Polytrichum) family a somewhat similar charac- 

 teristic is found, the capsule wall, instead of being 

 round, having a certain number of comparatively 

 flat faces, with corresponding angles, varying in 

 the different species from four to six, and running 

 up the whole length of the capsule. A reference 

 to Plate IV. a, fig. 13, will show more clearly what 

 I mean. 



Again, the position of the capsule with regard 

 to the leaves varies in different plants, and affords 

 a further guide in the naming of specimens. As 

 a rule, the fruit-stalk is long, and thus the 

 capsule is raised well above the leaves from the 

 midst of which it springs; it is then said to be 

 exserted, as in Plate II. figs. 9 and 10. But in 

 many cases the fruit-stalk is so short that it does 

 not lift the capsule above the level of the sur- 

 rounding leaves, as in fig. 11 of the same plate, 

 and here the capsule is consequently said to be 

 immersed. Plate IV.a, figs. 4 and 5 are other 

 instances of immersed capsules. 



The latter figure also exemplifies, with excep- 

 tional clearness, a point in the structure of the 

 capsule that may receive a passing word of notice. 

 In many cases, 'when the capsule is examined with 

 the microscope, a very distinct dark patch is 

 seen in the centre of it, evidently betokening 

 some part of the internal structure. This indi- 



