Metaphyta Polytrichu m. 103 



show this amount of differentiation. Whilst a few possess a 

 strand of elongated thick-walled cells in the axis of the stem, 

 many have only thin-walled medullary parenchyma. 



The stem of the moss may branch, whilst not in- 

 frequently a shoot or stolon, which may run along under- 

 ground, or just on the surface, may be given off. The stolon 

 usually takes root at some little distance from the parent 

 plant, and forming an upright stem begins life indepen- 

 dently. 



The roots of the moss are more correctly termed rhizoids, 

 as being the organs by which the thallus fixes itself to, and 

 absorbs nourishment from, the ground. The rhizoids spring 

 in a tuft from the base of the stem, differing, therefore, 

 markedly from the continuation of the stem below ground, 

 to which the term root is applied 



11 ric. 32. Polytrichiim comtm*:ie, 



in most Of the higher plants. \\ hen TRANSVERSE SECTION OF THE 



STEM. 



examined microscopically the rhi- 

 zoids are found to be merely cellu- 

 lar outgrowths from the epidermis, 

 and do not contain any of the sub- 

 jacent tissues. They correspond to 

 the epidermal hairs which are found 

 so abundantly springing from the 

 various organs, more especially of 

 flowering plants. The rhizoids, 

 unlike the stem, branch very freely, 

 and usually form a very dense mat- 

 ting below ground, or just on the surface. The cells forming 

 the rhizoids are elongated, and contain granular protoplasm, 

 oil globules, &c. enclosed in an orange-coloured or brown 

 cell-wall, the outer surface of which becomes gradually 

 clothed with particles of the soil. 



The leaves are also merely cellular outgrowths of the 

 stem, and are composed of almost undifferentiated paren- 

 chyma, the cells of which, however, contain chlorophyll in 

 addition to the ordinary constituents of such cells. In form 



