liedral apical cell has the usual three sets of lateral segments 

 and the outer ones that contribute to the root-cap. 



The cotyledon of (rlelcJienid, especially in the section Mer- 

 tensla, differs from that of most ferns. In the majority of ferns 

 the cotyledon is fan-shaped, the result of an eai'ly dichotomy. 

 In Gleichenia the original apex seems to persist, and although 

 the young cotyledon approximates the fan-shape of the typical 

 cotyledon, it is not easy to determine whether the small 

 fan-shaped terminal section is the result of the forking of 

 the primary branches or is really the primary leaf-apex. The 

 cotyledon thus shows something of the marked apical growth 

 that characterizes the later leaves of most species of the section 

 Mertensia. Figs. 55 — 58 (PL X) show different stages of the develop- 

 ment of the cotyledon. The definite apical cell of the young 

 cotyledon cannot be made out in the later stages and its place 

 seems to be taken by a group of narrow marginal cells (PI. XIV", 

 Figs. 124, 125). Whether one of these may be the real apical cell 

 it is hard to say, but it seems more probable that there is at 

 this time no single initial-cell. The marginal cells, seen in 

 longitudinal section, closely resemble the apical cells of the 

 prothallium (PI. XIV, Fig. 123). 



At the time the cotylodon is ready to emerge the rudiment 

 of the second leaf can usually be recognized (PI. XIV, Fig. 1 2 1 , L -). 

 This is not placed directly opposite the cotyledon, but at a 

 distance of about one-third the circumfei'ence of the stem. 

 Like the cotyledon it shows a distinct two-sided apical cell. 

 At the base of the second leaf, while it is still very small, the 

 second root appears (PL XIV, Fig. 121, II-). The initial cell, like 

 that of the later roots, arises fVom an endodermal cell of the 

 stem bundle. The initial cell is cut out ])y intersecting walls 

 and soon begins to divide, and later the young root breaks 

 through the overlying tissues at te base of the leaf. 



As we have already seen the first leaf, at least in O. (lic/io- 

 toma and (!. pectinaUi, shows something of the protracted apical 

 growth of the later leaves. The apex of the young cotyledon 

 is bent over, and the appearance of the cells is shown in 



