. Carnegie Institution of Washington publication. THE OLDER SPOROPHVTE 167 For a long time sections of the stem show this single central bundle of crescentic form, at first derived from the coalescence of the third, fourth, and fifth leaf traces, but continued upward in the same form and added to by the addition of the traces from the subsequent leaves. This crescentic stele, which, for convenience may be spoken of as the stele of the stem, is entirely of foliar origin. The crescent nevei becomes completely closed and its opening in the earlier stages of development can not be properly called
. Carnegie Institution of Washington publication. THE OLDER SPOROPHVTE 167 For a long time sections of the stem show this single central bundle of crescentic form, at first derived from the coalescence of the third, fourth, and fifth leaf traces, but continued upward in the same form and added to by the addition of the traces from the subsequent leaves. This crescentic stele, which, for convenience may be spoken of as the stele of the stem, is entirely of foliar origin. The crescent nevei becomes completely closed and its opening in the earlier stages of development can not be properly called a foliar gap. The parenchyma which is inclosed within its curve belongs from the first to the ground tissue and is not part of the stele. Some of the surrounding cells show traces of the typical endodermal markings and it is perhaps safe to say that the stele is bounded by an endodermis, as Farmer states is the case in Angwpteris and Brebner in D. simplicifolia. The limits of the endo- dermis, however, especially upon the concave side of the stele, are very vague. The stele, after the complete fusion of the three leaf traces, may perhaps best be described. Fig. 151. Four longitudinal sections of a young sporophyte of Darurn elliptica. X 18. The fourth leaf, /4, has the stipules well developed; r3, sections of the third root, m, mucilage duct; it, stipules. as concentric in structure, with phloem developed all around the xylem, but there are probably traces of phloem also between the three xylems which represent the three confluent leaf traces. In the older portions of the stem the bundles become still more completely fused and the compound bundle is oval in outline, but still shows plainly the three xylems of its constituent leaf traces (fig. 150, G). In this region the endodermis is rather better developed than it is higher up, but its limits are still rather vague. At this level the traces of the leaves, I and 2, are still free, but have approached nearer to the central bundl
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