168 



THE MAR VII I \I.I s 



core, but are more or less scattered, with thin-walled elements between. After 

 fusion of the second leaf trace with this is complete, the section ot the stem shows 

 only two bundles, representing the two first leaf traces, and finally (fig. 150,// and/) 

 the section of the stem shows the condition already described for the sporophyte 

 with but two leaves. These finally merge into a single primary axial bundle (/), 

 which, followed downward, merges imperceptibly into the stele of the primary root. 

 Near the middle of these lower sections can be seen a section of the second root, 

 which pursues a downward course through the cortical tissue for a very long distance, 

 but finally emerges and grows downward, side by side with the primary root. The 

 third root (fig. 150, G, r J ) emerges much higher up and breaks through the cortex 

 at about the level of the junction of the three youngest leaf traces. 



Fig. 153 shows the details of the central tissue from the same sporophyte as 

 that just described. A passes through the stem apex and shows the apical cell cut 

 somewhat obliquely, and near it the section of the trace from the tilth leaf. D is a 

 section of the fourth leaf trace from the same level. This shows but two tracheids 

 at a point near the inner limits of the bundle, while on the outer side there is a con- 

 spicuous curved line of protophloem cells. B is a section taken somewhat lower 

 down and shows the bending in of the leaf trace as it descends into the stem. This 

 is still more marked in the fifth leaf trace, which, at this level, has a crescentic form. 



Fig. 152 



A. Apex of fifth leaf from sporophyte shown in fig. 151. X150. 



B. Stem apex of same. 



C. Base of third root, showing triarch bundle and ring of sclercnchyma in cortex. X90. 



but no permanent elements yet developed. It is probable that a portion of this 

 crescentic mass of procambium represents the sixth leaf trace. The fourth leaf 

 trace at this point shows three tracheids which are decidedly larger than those 

 higher up, and still lower down the tracheids increase still more in size and several 

 tannin cells can be seen in contact with them. The section of the fourth leaf trace 

 is connected with the large but undifferentiated trace of the fifth leaf by an isthmus of 

 procambium cells, so that the sections of the two bundles form the crescent-shaped 

 section, similar to that seen lower down ( fig. 153, 6). The tracheary elements of the 

 fused portion of the fourth leaf trace are noticeably larger again than those in the 

 free portion of the leaf trace. We now notice, for the first time, traces of the mucilage 

 ducts which afterwards become so conspicuous in the stem. I Inst- first appear in 

 section as rounded cells (m), and it is evident, as Farmer has shown in Angiopteris, 

 that the earliest mucilage canals are of lysigenous origin, i. e., the) are formed by a 



