THE EMBRYO 



41 



bud and the young stem apex can already be recognized, and these have apparently 

 developed quite independently of each other. The leaf rudiment, B, lies nearer the 

 bundle of the main root and may perhaps have taken its origin from a single endo- 

 dermal cell, but this could not be certainly determined. The young leaf soon forms 

 a slightly projecting conical body, composed of a few cells with conspicuous nuclei, 

 separated from the adjacent root tissue by a small space. At this stage it is not quite 

 clear whether the apical cell has been developed, but later stages show the presence 

 of an unmistakable apical cell of approximately tetrahedral form. Lying nearer 

 the periphery of the root is the young stem apex, composed of a small group of 

 meristematic cells, one of which is unmistakably the initial cell for the stem. This 

 apical cell is truncate below and the base is broader than the outer free face. Above 

 the stem apex can be seen the cavity which separates the outer tissues of the young 

 bud from the cortical tissue of the root. 



Fig. 24, D, shows two transverse sections of a bud of about the same age as the 

 one just described. No. i passes through the stem apex and shows the conspicuous 

 triangular apical cell; No. 2 shows a section of the leaf above the level of the stem 

 apex with the basal tissue of the leaf extending around the stem region. This is the 

 beginning of the hollow stipular sheath which incloses the stem apex of the bud and 



Fig. 25. — Ophioglossum moluccanum. 



A. Bud about to break through primary root; /, first leaf j jf, stem apex. X about 80. 



B. Apex of leaf more highly magnified. 



C. Transverse section of a young bud passing through base of leaf, /. X 1 50. 



D. Section of same passing through stem apex, x. 



E. Transverse section of stem apex from an older sporophyte. The apical cell is four-sided. 



which is SO conspicuous a feature in the stem apex of the older sporophyte. Probably 

 the large central cell in the section of the leaf shown in No. 2 is the apical cell, but 

 this is not quite certain. 



A transverse section of a somewhat older bud (fig. 25, C) shows a narrow cleft 

 at the base of the leaf in front, opening into a cavity within which the stem apex lies. 

 It is impossible to say exactly how much of this stipular sheath really belongs to the 

 leaf base and how much is derived directly from the adjacent cortical tissue of the 

 root, since the tissues of the leaf base merge insensibly into the latter. From this 

 time on, each new leaf develops this conical stipular sheath, which incloses the stem 

 apex and the next youngest leaf, and which has so often been described in the older 

 sporophyte. 



If a median section of the young bud is examined just before the bud breaks 

 through the overlying tissues of the root (fig. 25, A), it can be clearly seen that the 

 leaf, which now has the form of an elongated cone, lies above the level of the young 

 stem apex, and by this time the differentiation of the vascular bundle of the leaf is 

 well advanced. This bundle connects with the vascular bundle of the primary root 



