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A TEXTBOOK OF THEORETICAL BOTANY 



of branched, multicellular filaments called the protonema. The branches 

 of the protonema elongate very rapidly, growing by means of an apical cell, 

 and in a short while produce a luxuriant, green, velvety growth. The 

 protonema is characterized by its discoid chloroplasts and oblique transverse 



TOOTH OF 

 OUTER PERISTOME 



OPERCULUM 



ANNULUS CELLS 



THICKENED RIM 



CAPSULE WALL 



Fig. 414. — Mnium hornum. Vertical section through 

 annulus and rim of theca. {After Lorch.) 



walls, which easily distinguish it from a Green Alga. From this protonema 

 numerous small multicellular rhizoids are developed, and we find that in 

 structure these rhizoids resemble closely those produced from the base of 

 the leafy plant. They also have oblique cross walls. On short branches of 

 the protonema tetrahedral apical cells develop (Fig. 415), and each of them 

 forms the growing apex from which a young Moss plant develops. The 

 protonemata are long-lived, and continue active long after the Moss plant 

 has begun to develop. It is by their means that the large tufts or mats of 

 Moss plants which we so often meet with are produced, and it is owing to 



