MOSSES AND LIVERWORTS. 123 



the cells containing large and clearlj^ defined chlorophyll 

 bodies. Notice their position in the cells ; does it appear 

 to be constant? 



A little attention will show that the leaf is not a simple 

 plate of cells throughout. Examine the midiib and com- 

 pare with the axial cylinder of the stem. 



III. Look for other kinds of leaves, scale leaves, of 

 frequent occurrence, especially on the lower part of the 

 stem, and perichsetial leaves, forming a rosette, usually at 

 the apex of fruiting stems.^ 



Fructification. 



I. Taking any of the mosses in the collection that are 

 in fruit — several species if possible — observe 



1. The slender stalk, seta, on which is borne 



2. The capsule, containing spores. 



Compare the capsules of different species as to size, 

 form, color, and other features. 



II. Make a thorough study of the parts composing the 

 capsule, using the compound microscope when needed. 



1. The calyptra, commonly a thin membrane covering 



the apical part of the capsule ; rarely, as in 

 Polytrichum, a thick hairy cap. Notice the form, 

 differing in diiferent genera. 



2. The operculum, in most genera a conical lid, fitting 



closely to the end of the capsule, but thrown off 

 when the latter is fully ripe, thus permitting the 

 scattering of the spores. 



3. Lightly covered by the operculum when it is in 



place, but showing conspicuously when it is re- 



1 For further suggestions cf. Arthur, Barnes, and Coulterj Plant Dissec- 

 tion, p. 84 et seq. 



