428 MOSSES AND FERNS chap. 



octant, in contact with the foot. Hanstein and Arcangeli re- 

 gard these as part of the foot, and physiologically they no doubt 

 are to be so considered, but morphologically they are beyond 

 question segments respectively of the stem and second leaf. At 

 first these are not distinguishable from each other, but the divi- 

 sions in the latter are usually (in Pilularia) less regular, and 

 the apical cell early lost. It may, however, develop a regular 

 three-sided apical cell, like that of the later leaves. The earlier 

 segments of the stem apex are larger than the subsequent ones, 

 and the broadly tetrahedral form of the primary octant is re- 

 duced to the much narrower form found in the older sporophyte. 



The Root 



The first wall in the root quadrant strikes the basal wall 

 at an angle of about 60°, so that the octants are of very unequal 

 size (Fig. 250, C), and the larger one, as in other similar cases, 

 becomes at once the initial cell of the root, which in both genera 

 shows the same regular divisions that characterise the Poly- 

 podiacese. The segments of the root-cap do not form any peri- 

 clinal walls, and remain single-layered. The root, like the 

 cotyledon, is traversed by regular air-chambers, and its trans- 

 verse section resembles very closely that of the leaf. These air- 

 chambers appear while the root is very young, and at a point 

 between the endodermis and the cortex. The latter is at this 

 stage divided into but two cells, the outermost of which by a 

 further tangential division becomes two-layered, the outer 

 forming the epidermis, and the inner by similar divisions be- 

 comes three-layered. The two outer layers divide by radial 

 walls, but the inner ones divide only by periclinal walls, and 

 form one-layered lamellae separating the air-spaces and connect- 

 ing the endodermis with the outer cortex. 



The Foot 



The first divisions in the foot quadrant follow closely those 

 in the root, but this regularity soon ceases, and after the first 

 divisions no definite succession in the walls can be distinguished. 

 The foot remains small, but, as we have seen, the first segments 

 of the lower epibasal octants practically form part of it, and 

 doubtless all the lower cells are concerned in the absorption of 



