THE YOUNG SPOROPHYTE 



155 



that the leaves arise from the segments of the apical cell of the stem, and their 

 tissues are therefore indirectly derived from the stem apex, we may say that the stem 

 apex takes no part in the differentiation of the fibro-vascular system, which in the 

 young sporophyte is composed entirely of the leaf and root traces. 



THE ROOT. 



Only a small number of sections of the primary root were obtained in Marattia 

 douglasit, and these showed some variation, so that it is not possible to state posi- 

 tively what is the typical form of its apical cell, but there is no question that the 

 primary root grows from a single initial cell, as in the other genera. In longitudinal 

 section it appears oblong, with a broadly truncate base from which segments arise, 

 as well as from the lateral faces. There seem to be regularly four sets of lateral 



Fig. 138. 



A. Nearly median section of a young sporopliyte of Danaa jamaicensis, passing through stem apes. X about 40. 



B. Another section of same, passing through second leaf, l^ 



C. Section of another similar sporophyte cut at right angles to that shown in A and B, and showing continuity 



of bundles of cotyledon and primary root, pr, garaetophyte; sc, scales. 



segments, although cross-sections of the apical cell sometimes appear almost trian- 

 gular. The root cap is formed in part from segments derived from the outer face 

 of the apical cell, in part from similar segments cut off from the outer portion of 

 the youngest lateral segments of the apical cell. The central cylinder of the root 

 is formed in part from the basal segments of the apical cell, but the lateral seg- 

 ments also contribute to it (fig. 141, D). 



In Angiopteris (fig. Ill, C) the apical cell in the earlier stages of the root may 

 appear triangular in longitudinal section, but in the later stages it is usually more or 

 less truncate. 



The primary root in Kaulfussia, in the few cases where satisfactory sections 

 were made of it, did not show the tetrahedral apical cell, but this was truncate at the 

 base and in cross-section appeared four-sided (fig. 142). In this respect it seems to 

 approach Marattia. The primary root in all of the Marattiaceas is ordinarily diarch; 



