326 MOSSES AND FERNS CHAP. 



are all spiral, and occupy the centre of the concentric bundle, 

 and from these growth proceeds centrifugally. The elements 

 of the phloem are poorly differentiated, and in this stage no 

 true sieve-tubes could be detected. While a definite bundle- 

 sheath can scarcely be made out, the limits of the bundle are 

 clearly defined. The venation of the cotyledon is dichotomous, 

 corresponding to the dichotomous branching of the lamina. 



The vascular cylinder of the young stem is solid, and is 

 mainly composed of short and broad scalariform tracheids, but 

 in the centre of the bundle are some small spiral and reticulate 

 ones. The phloem at this stage is not well developed, and does 

 not show perfect sieve-tubes. The bundle sends a branch to 

 the second leaf, but is continued beyond the point of contact, 

 and develops tracheids above the point of union before the first 

 ones are formed in the leaf. In this early stage the bundle- 

 sheath is very poorly differentiated in the stem, but becomes 

 better marked as the plant develops. 



The primary root is monarch, and the tracheary tissue com- 

 posed of short pointed tracheids with irregular scalariform 

 markings. These are surrounded by one or two layers of 

 narrow cells with oblique transverse septa. The calyptra is 

 soon penetrated by the cotyledon, which, instead of growing 

 straight up through the prothallium, as it does in Marattia, 

 breaks through upon the ventral side and then bends upward 

 between the lobes in front (Fig. 179, E). The root bends 

 down and penetrates the earth, and very soon after, the pro- 

 thallium dies. The epidermis of the cotyledon produces small 

 glandular hairs, and that of the root numerous root-hairs. 



The second leaf is directly traceable to one of the primary 

 stem octants, and may be either regarded as one of the primary 

 members of the embryo, or as the first segment of the stem. 

 Its development corresponds exactly to that of the cotyledon, 

 as 'it does in its fully-developed state. The second root arises 

 endogenously, like all the later ones, and its apical cell is formed 

 close to the point of union of the bundles of the leaf and stem, 

 and probably, as in the later roots, is derived from a cell of the 

 endodermis. 



The new leaves arise in regular succession from the segments 

 of the apical cell of the stem and up to the fifth or sixth, and 

 possibly later the first division of the leaf is dichotomous, and 

 the pinnate form of the later leaves is gradually attained, as in 



