THE BRYOPHYTA : MUSCI, THE MOSSES 



417 



Fig. 399. — Mnium hortnim. Antheridial 

 heads on gametophyte showing the in- 

 volucre of large leaves. Enlarged. 



cells, known as hydroids (Fig. 400), and an outer tissue termed the cortex, 

 composed of wider cells, with brownish-coloured walls, containing some 



Lateral bud 



Central strand 



Fig. 400. — Mnium hoytiutu. Transverse section through 

 stem of the gametophyte, showing axial strand of 

 hydroids and thickened outer cortex. Note the 

 absence of any supply of conducting tissue to the 

 lateral bud. 



Starch grains and chloroplasts. The innermost layer of the cortex may 

 be distinguished by its greater resistance to the swelling action of sulphuric 

 acid, and although it is not justifiable to regard this layer as comparable 

 with an endodermis (see p. 457), we realize that already in these simple 



