VI MOSSES {MUSCI): SFHAGNACEJE—ANDRE.'EACEyE 173 



an accidental resemblance. The closely-set stems branch freely ; 

 the leaves, with three-eighth divergence, are either with a mid- 

 rib {A. riipestris) or without one {A. petropJiild). 



The growth of the stem is from a pyramidal apical cell, as 

 in Sphagnujii, and probably the origin of the branches is also 

 the same as in that genus. The growth of the young leaves is 

 usually from a two-sided apical cell, but another type of growth 



A 



Fig. 82. — Andrecea pctrophila (Ehrh.). A, Plant with ripe sporogonium, x lo ; 1), median 

 section of nearly ripe capsule, X 80 ; ps, pseudopodium ; col, columella. 



is found where the apical cell is nearly semicircular in outline, 

 and segments are cut off from the base only. These two forms 

 of apical growth apparently alternate in some instances in the 

 same leaf. The originally thin walls of the leaf cells later 

 become thick and dark-coloured, whence the characteristic dark 

 colour of the plant. 



The stem in cross-section shows an almost uniform struc- 

 ture, and no trace of the central conducting tissue of the higher 

 Mosses can be found. The outer cells are somewhat thicker- 

 walled and darker-coloured, but otherwise not different from 



