THE OLDER SPOROPHYTE 



161 



outside the prothallium; the cotyledon at this time is still very small and the lamina 

 is scarcely developed. The root apex does not show in the section figured and all 

 that can be seen is the upper portion of its stele, which joins the two young vascular 

 bundles that extend respectively into the cotyledon and the second leaf, which can 

 already be recognized. The greater part of the young sporophyte is made up of 

 large thin-walled cells. Figure 121, B, shows a median section of the young cotyledon 

 from this same embryo, which is strongly bent over the stem apex. It is possible 

 that the square terminal cell, which in the drawing has the nucleus indicated, is the 

 apical cell of the leaf, but this is not at all certain. The outer part of the cotyledon 

 is made up of large thin-walled cells like those which compose the bulk of the 

 sporophyte, but at its apex there is active cell division, and traversing the young 

 cotyledon and placed somewhat toward its inner side, can be seen the primary 

 vascular bundle, made up of elongated procambium cells. This bundle can be 

 easily followed down into the body of the sporophyte, where, as we have seen, it is 



Fig. 145. 



Transverse sections of a very young sporophyte of Datttsa jamaicertsis. X150. 



A shows cotyledon apex; C, apices of the stem and second leaf; G shows root apex. 



continued without interruption into the stele of the primary root. The stem apex, 

 which does not show in the figure, is in a slight depression close to the base of the 

 cotyledon and shows, as usual, a single deep apical cell. Nearly opposite the cotyledon 

 is the beginning of the second leaf (/ ^); this is shown in median section in fig. 121, B. 

 The group of narrow columnar cells that compose its apex does not show a recog- 

 nizable single initial cell. A short distance below its apex, the procambium of its 

 vascular bundle becomes differentiated and is continued downward until it joins 

 the bundle from the cotyledon. The tissue arising above the junction of these two 

 bundles and continuing upward into the apex of the stem is composed of absolutely 

 undifferentiated parenchyma and there is no evidence at all of any stelar tissue in 

 the stem above the junction of these two primary leaf traces; indeed, the stem apex 

 lies decidedly on one side of the plane which traverses the vascular bundles of the 

 two leaves. Fig. 145 shows a number of cross-sections from a series taken from a 

 large embryo of Dancea jamaicensts, before the emergence of the cotyledon {A\ 

 11 



