THE YOUNG SPOROPHYTE 75 



apex, which is doubly protected by these scales and its complete inclosure in the 

 young leaf bases. It is possible that these scales secrete some mucilaginous sub- 

 stance, although there was no evidence of this in the stained sections. 



In this plant the internodes were quite solid and there was no trace of the large 

 lacunae which were described for the younger plant. Whether the presence of the 

 lacunae is due to any differences in the environment remains to be seen. The speci- 

 mens were all collected under apparently the same conditions, but it is possible that 

 there may have been differences in the amount of water in the soil in which they were 

 growing, and this difference in the amount of water may have something to do with 

 the development of the lacunae. 



The root at the base of the third leaf was cut transversely and was in a very 

 early stage of development. The root was still completely buried in the cortex and 

 the stele still imperfectly developed, but showing its connection with the stele of 

 the fourth leaf above the junction of the third leaf trace with the stele of the inter- 

 node. No tracheary tissue was developed and the course of the leaf trace was but 

 little disturbed by the formation of the root. 



In longitudinal sections taken from a much older sporophyte (fig. 48, C, D) 

 the arrangement of the organs at the apex is seen to be exactly the same as in the 

 younger plants, but of course the parts were all larger. The youngest leaf (/ ' ) still 

 resembles in form and size the corresponding leaf in the younger stem, but the next 

 older leaf is relatively broader than the early leaves of the younger sporophyte, and 

 although the stipular sheath is now well developed the upper portion of the leaf 

 is still quite undifferentiated and the apex is scarcely bent forward at all. The 

 resemblance, therefore, to the young leaf of Botrychium lunaria is even more 

 marked than it is in the younger sporophyte. The apical region of this young leaf 

 is occupied by an epithelium-like layer of columnar cells, and it is doubtful whether 

 any one of these can be certainly denominated the apical cell. Somewhat the same 

 doubt exists also as to the point of a single initial cell in the youngest leaf. In the 

 latter there was some shrinkage in the group of large meristem cells at the apex, 

 which made it still more difficult to decide this point, but a median section showed 

 somewhat indistinctly a single cell, apparently triangular in outline, which from its 

 form and the arrangement of the adjacent cells may very well have been the apical 

 cell. The small group of meristem cells forming the stem apex is crowded in between 

 the base of the youngest leaf and the elongated ridge which surrounds the stem apex 

 upon the ventral side. In consequence of this crowding the outer faces of the 

 apical cell and its youngest segments are very small. The base of the apical cell 

 is more than twice as broad as its free outer face. The ventral face of the apical 

 cell is convex and the young segments cut off from it are strongly curved. The inner 

 or basal wall is oblique, so that the axis of the young cells in the tissue below the 

 apical cell makes an angle with the long axis of the apical cell. 



Below the apical region may be seen the section of the large central stele of the 

 internode. This is composed, apparently, of two strands of procambium separated 

 by a broad band of pith. As Farmer pointed out, in the older plant there is no 

 question that procambium tissue is developed upon the ventral side of the bundle 

 which extends into the apical region and which is, apparently, not connected with 

 the leaf traces. From this he believes that the stele is really a cauline structure. 



A study of the cross-sections, however, as will be presently seen, shows that 



this ventral tissue really does belong to the leaf traces, although it is possible that 



-the basal tissue of the roots may add to it in part, but I have not been able to 



satisfy myself that any of this stelar tissue can be properly assigned to the activity 



of the stem apex. 



