62 



THE OPHIOGLOSSALES 



of wood, which is surrounded by the phloem, although the latter is much less 

 developed upon the inner side than upon the outer and the bundles thus approach 

 the collateral condition found in the trace lower down. Small protophloem ele- 

 ments occur in the outer part of the bundle and are continued part wa}' around 

 toward the lower side, to the point where the two bundles are beginning to fuse, 

 but here they are no longer visible. 



The second leaf shows no lacunas and the base of the petiole is more nearly 

 cylindrical than is that of the cotyledon. Like the latter, the petiole contains two 

 vascular bundles which at the level of this section were still quite distinct, and the 

 permanent elements were just beginning to form. The stipules in the second leaf 

 completely inclose the third, but there is a very narrow slit in front where the two 

 stipules meet. The next section figured is taken just above the stem apex and cuts 

 through the youngest (fourth) leaf. The two bundles of the petiole of the third leaf 

 are evidently still quite separate, but closely approximated, and as yet show no per- 

 manent tissue. The stipules of the third leaf are just becoming evident. At the 

 level of the stem apex the bases of the third and fourth leaves are completely united. 



Fig. 43. 



Series of transverse sections of a young sporophyte of Botrychium virginianum^ showing union of leaf traces to form vascular 

 cylinder. D and E show the separated leaf traces which unite further down; K shows the bundle of the axis near 

 its junction with the stele of the primary root. 



and the base of the second leaf is also partially fused with these. The two bundles 

 from the second leaf are now beginning to unite to form the single leaf trace, while 

 in the third leaf the process is complete and a single oval mass of procambium cells 

 marks the position of the single trace of this leaf. On the opposite side of the 

 apical meristem is a similar but less developed mass of procambium, representing 

 the trace from the young fourth leaf. 



For some distance below the stem apex the two bundles of the third and fourth 

 leaf respectively are quite distinct, and are separated from each other by a mass of 

 large-celled pith. Lower down the two bundles approach and coalesce, and on the 

 side of the second leaf trace (which is turned away from the third one) a group of 

 actively dividing cells can be seen which forms the beginning of the fifth leaf trace, 

 although the leaf itself can not be recognized at the summit. These three masses 

 of procambial tissue, viz, the young traqes from the third, fourth, and fifth leaves, 



