230 



XVIII. STRUCTURE OF THE BRYOPHYTA. 



If the cross-section has passed through an injured part of the 

 stem of Mnium, the place is seen not to be covered with cork, 

 since this cannot, with a few exceptions, be formed by the Cryp- 

 togamia ; on the other hand, the walls of the cells bordering the 

 wound are thickened and browned, and so, apart from their broader 

 cavities, simulate the other surface cells. 



Near the surface can be seen, in the cross- section, isolated 

 small strings of thin-walled cells, which in coloration also resemble 

 the elements of the central conducting bundle. These are the 

 foliar conducting bundles, which have " blind " endings in the 



FIG. 91. A moss, Funaria hyyro'inetrica. A, germinating spores ; ', root-liair, or 

 rhizoid ; s, exospore (x 550). B, part of a developed protonema, about three weeks 

 after germinating ; h, a procumbent primary shoot, with brown wall and oblique septa ; 

 from this arise the ascending branches, having limited growth. K, rudiment of a 

 leaf-bearing axis with w, rhizoid or root-hair (x about 90). (After Prantl.) 



cortex of the stem, though in the more fully organised Poly- 

 trichum 1 they join on to the axial conducting bundle of the stem. 

 Leaf of Mnium. A leaf, which we examine without prepara- 

 tion in a drop of water on the object-slide, shows a unilamellar 

 lamina, and a multilamellar midrib. This latter ends in a terminal 

 tooth, which consists of a number of rhombic cells. The cells of 

 the midrib are very elongated, the peripheral cells contain chloro- 

 phyll grains. The lamina of the leaf is unilamellar ; it consists of 

 polygonal chlorophyll containing cells. The seam -like edge of the 

 leaf is formed of elongated, strongly-thickened cells. The outer- 



1 In Polytrichum, the inner part of the axial conducting bundle is com- 

 monly collenchymatous. [ED.] 



