;o 



SECOND GROUP. MUSCINEAE. 



and Buxbaumieae and others is scarcely one millimetre in height, the stem of the 

 larger Hypneae and Polytricheae often two, three or more decimetres ; it may be even 

 longer, as in Sphagnum, if not in one axis yet by innovation and the formation of 

 sympodia. The thickness of the stem does not vary so much : it may be one-tenth 

 of a millimetre in the smallest, and scarcely more than one millimetre in the thickest 

 stems; but its compact tissue, coloured externally, is very firm, often rigid, always 

 very elastic, and capable of long resistance to decay. 



The rhizoids (root-hairs) play a very important part in the economy of the 

 , . Mosses. It is only in the Sphagnaceae, 



which differ in many other points from 

 the rest of the class, that the rhizoids 

 are few and small ; in most of the other 

 Mosses they appear in great numbers, 

 at least from the base of the stem, and 

 often clothe it all over with a thick red- 

 dish-brown felt. Morphologically there 

 is no sharply defined line of distinction 

 between the rhizoids and the proto- 

 nema 1 ; they originate as tubular out- 

 growths of the superficial cells of the 

 stem, elongate by apical growth, and 

 are divided by obliquely transverse walls ; 

 their wall is hyaline at the growing end 

 and grows into intimate union with parti- 

 cles of matter in the soil ; these are after- 

 wards detached, the wall becomes thicker, 

 and assumes the brown colour of the 

 rhizoids that are above ground. The 

 cells contain much protoplasm and some 

 drops of oil, and not unfrequently chlo- 

 rophyll also (Fig. 123, j??). The rhizoids 

 in many Mosses branch copiously be- 



FlG. 123. A young plant of Barbula m, with a rhizoid h, the noqfVj fVic. q n il forming oftentimes a 

 growing extremities of which v v are covered with particles of soil ; J -Ml, * Ullg OH< 



thick inextricable felt; they can also 

 form a close turf in the same way above 

 ground to serve as a soil for future 



generations. In Atrichum and other Polytrichaceae the thicker rhizoids become 

 twisted together like the strands of a rope ; their branches do the same, and only 

 the latest and finest ramifications remain free. 



The vegetative propagation in the Mosses is more varied and fruitful than in 

 any other portion of the vegetable kingdom. It has this peculiarity, that the forma- 

 tion of a new leafy stem is always preceded by the production of a protonema, even 



1 The rhizoids appear to be essentially distinguished from the protonema produced from the 

 spore only by a more sparing formation of chlorophyll, by their brown walls, and by the tendency to 

 grow downwards ; the protonema developes some of its branches as rhizoids, and the rhizoids in turn 

 can develope single branches as protonema rich in chlorophyll and growing upwards. 



