THK YOUNG SPOROI'HYTE 



61 



evidently slow and there is usually a good deal of difference in the stage of develop- 

 ment in the three segments composing a single cycle. The first division in each 

 of the lateral segments cuts off a small inner cell from a large outer one, and the 

 latter is then divided into two by an anticlinal wall. The divisions were not followed 

 beyond this stage and the limits of the segments comprising the second cycle can 

 not be easily recognized, as by this time the youngest leaf begins to grow and the 

 stem apex is thus crowded into a very small area between the bases of the two 

 youngest leaves. The shallow mass of meristematic tissue comprising the stem apex 

 merges gradually into the large-celled parenchyma which makes up the pith cylinder 

 inside the hollow stele of the axis. 



Longitudinal sections of a much older sporophyte are shown in fig. 42. 



Except for the vascular bundles, the whole of the tissue of the young sporophyte 

 is composed of large-celled parenchyma which, especially in the region belonging 

 to the foot, contains large quantities of starch. 



The form of the young leaves in B. virgtnianum is very different from that 

 in B. lunana. In the former the young leaf is bent forward over the stem apex and 

 the apical cell is at the tip of this bent-over portion. In B. lunana, however, the 



Fig. 42. 



Three longitudinal sections of a young sporophyte of Botrychium virginianum, with several leaves. 

 per, absciss layer of periderm; /, /, the youngest leaves; sh, stipular sheath. Xio. 



bent-over portion becomes the stipular region and the apical cell of the young leaf 

 arises in the convex upper portion, so that the leaf grows straight upward instead 

 of being bent over as it is in B. virginianum. The latter species in this respect 

 resembles the Marattiaceae. 



The stipules in B. virginianum are lateral structures which extend around the 

 next youngest leaf and the stem apex, but the sheath has a narrow cleft in front, so 

 that we may really speak of two stipules instead of a single stipular sheath (fig. 

 42, A). In this respect also there is a strong resemblance to the Marattiaceae. 



Fig. 43 shows a series of transverse sections of a young sporophyte of B. vir- 

 ginianum in which the fourth leaf was just evident. Fig. 43, A and B, are near 

 the base of the fourth leaf and show the arrangement of the first four leaves. The 

 base of the cotyledon (cot) is a good deal flattened and the petiole is seen to be 

 traversed by very conspicuous lacunae, reminding one of those in the cotyledon of 

 Ophioglossum moluccanum. The conspicuous stipules can be seen extending 

 partly around the group of younger leaves, but not completely inclosing them. The 

 two vascular bundles of the petiole are beginning to unite to form the single leaf 

 trace which is found lower down. The xylem in each bundle forms a broad band 



