320 MOSSES AND FERNS chap. 



Throughout the life of the sporophyte no vessels are formed, 

 but only tracheids, as in nearly all Ferns. In the cotyledons 

 the tracheids are all spiral, and occupy the centre of the con- 

 centric 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 bundle 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 

 composed 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. i6i, E). The root bends 

 down and penetrates the earth, and very soon after the 

 prothallium 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 



