444 MOSSES AND FERNS chap, xiii 



the amount of this tissue is much greater and the lacunae less 

 conspicuous, or indeed even wanting. 



The epidermis, as is well known, contains great quantities 

 of silex, which gives it its very rough and harsh surface. This 

 is deposited either uniformly, as is usually the case in the 

 lateral cell walls, or in tubercular masses. Upon the inner 

 surface of the guard cells of the stomata it forms regular 

 transverse bars (Fig. 232). Upon the outer walls of the 

 epidermal cells the masses form either isolated bead - like 

 projections or these are more or less completely confluent. 



The stomata are peculiar in structure, and their development 

 was first correctly described by Strasburger.^ In E. telmateia 

 these only occur usually upon the foliar sheaths, but in species 

 with green internodes they are found principally upon the sides 

 of the furrows over the green hypodermal tissue.^ Before the 

 stoma proper is formed, the cell divides twice by longitudinal 

 walls (Fig. 232), and the original cell is thus divided into a 

 central one (the real stoma mother cell) and two narrow lateral 

 accessory cells. The central cell now divides again, and the 

 division wall splits in the centre as usual. A cross-section of 

 the young stoma (Fig. 232, D) shows that the walls by which 

 the accessory cells are cut off are inclined, so that the stoma 

 cell is broader at the bottom than at the top, and as develop- 

 ment proceeds the accessory cells completely overarch the 

 stoma, and in the older ones look as if they had arisen by 

 horizontal divisions in the primary guard cells. The accessory 

 cells show the same tuberculate silicious nodules upon their 

 outer walls as the other epidermal cells, and upon the inner 

 face of the real guard cells only are formed the regular bars. 

 Stomata are quite absent from the rhizome, and also from the 

 colourless fertile branches of E. telmateia. Compared with the 

 aerial stems, the rhizome shows a smaller number of vascular 

 bundles, and a corresponding reduction in the number of the 

 lacunae. 



Until the researches of Janczewski ^ and Famintzin * it 

 was supposed that the lateral branches arose endogenously. 

 Their researches, however, showed conclusively that this was 



^ Strasburger (l). 



^ Miss E. A. Southworth (i) found that in E. arvense they occur upon the ridges, 

 and upon the fertile as well as the sterile shoots. 



^ Janczewski (3). ■* Famintzin (i). 



