THE OLDER SPOROPHYTE 163 



stage to that shown in A , but cut at right angles to it, so as to show the continuity 

 of the bundles of the cotyledon and primary root, which together constitute the prima- 

 ry axial vascular bundle of the sporophyte, as they do in Ophioglossum moluccanum. 

 The similarity of such a section as that figured to the similar stage in 0. moluccanum 

 is sufficiently obvious. The stem apex is shown in fig. 140, A, and the rudiment of 

 the second leaf is shown in fig. 140, B. 



Figure 146 shows ten transverse sections from a series made from a young sporo- 

 phyte of D. jamaicensis of almost exactly the same age as that shown in fig. 138, B. 

 A is cut above the level of the stem apex and passes through the cotyledon and apex 

 of the second leaf. The arrangement of the cells at the apex of the latter suggests 

 the possibility of a single apical cell. The base of the petiole of the cotyledon is 

 much flattened and is made up of large, thin-walled parenchyma with no traces of 

 tannin cells or mucilage ducts. The vascular bundle is oval in outline and decidedly 

 collateral in structure. There is no recognizable endodermis, and I shall not 

 attempt to say whether the cells immediately surrounding the bundle should be 

 spoken of as endodermis or pericycle. Except for two small tracheids on the inner 

 side of the bundle the vascular bundle is composed of delicate tissue, apparently 

 parenchyma, but some of the larger elements undoubtedly represent sieve tubes. 

 Brebner states that the sieve tubes in D. simplicifolia (Brebner 3, page 524) do not 

 show clearly in sections mounted in Canada balsam, but when examined in other 

 media they show thick, glistening walls and pitted areas. This point was not further 

 examined in the species under consideration, but would probably agree with the 

 observations made by Brebner upon D. simplicifolia. 



Section B passes through the stem apex, whose apical cell is shown on a larger 

 scale in D. The cotyledon trace in this section shows three tracheids. In D the 

 section is made a short distance below the stem apex and shows the second leaf trace 

 bending in to join the trace from the cotyledon. The central part of the section is 

 shown more enlarged in E, and it is perfectly clear that the region immediately 

 below the apex and lying between two leaf bases shows nothing which can be 

 interpreted as a cauline stele. F and G show sections taken still further down, 

 illustrating the coalescence of the two leaf traces to form the single axial stele. In 

 G there is seen the first tracheid belonging to the leaf trace from the second leaf, 

 and in H the central bundle is complete and there are seen the two xylem masses 

 corresponding respectively to the two leaf traces. One of these, belonging to the 

 primary leaf trace, is more developed than the other one. The larger xylem mass 

 in this case had five tracheids and the smaller one three. / and / are transitional 

 stages between the bundle of the cotyledon and the root, and, proceeding down- 

 ward, the bundle becomes somewhat smaller and there is a reduction in the number 

 of tracheids, which, however, are plainly seen to be continuous in their development 

 with the two xylem masses in the central bundle of the stem, formed by the junction 

 of the two primary leaf traces, which maintain their identity until they merge into 

 the two xylem masses of the diarch root. Within the root itself the endodermis 

 surrounding the bundle is very conspicuous. The cells making up the endodermis 

 are of large size and the characteristic markings upon their radial walls are very 

 easily seen. The limits of the endodermis become much less clear in the transi- 

 tional region, and higher up it is difficult to make out a clearly defined endodermis. 

 Brebner figures a very irregular endodermis in the stem of D. simplicifolia, and 

 perhaps we may assume that a proper endodermis is present also in the young stem 

 of£>. jamaicensis, but it is certainly very inconspicuous, to say the least, in the central 

 region of the young sporophyte, in strong contrast to the very conspicuous endo- 

 dermis in the root. Farmer (Farmer 3) was able by treatment with sulphuric acid 



