THE YOUNG SPOROPHYTE 



151 



basal portion. The vascular bundle has a greater development of xylem than in the 

 other genera and the xylem forms a band of considerable extent in the oval section of 

 the bundle. The structure of the bundle is concentric, but, as in other cases, the 

 phloem is better developed upon the outer side. Below the free base of the cotyledon, 

 where the trace enters the stem, there is a reduction of the inner phloem, or the 

 inner phloem entirely disappears, and the bundle there becomes truly collateral. No 

 definite endodermis can be recognized and the tannin cells found in the cotyledon 

 oi Angiopteris are quite absent. 



Fig. 131. 



A. Section of petiole of cotyledon of Z)a«£Cd e////jr;c^. X75. 



B. The vascular bundle. X200. 



C. Section of a peltate scale. X75. 



The section of the petiole of the cotyledon in Danaa (fig. 131) is nearly cir- 

 cular, and the wings found in the other forms are almost entirely obhterated. The 

 ground tissue is composed of undifferentiated parenchyma, with no trace of tan- 

 nin cells. The vascular bundle is circular in outline, with a small group of three 

 or four tracheids placed somewhat toward the inner side of the bundle, but sepa- 

 rated from the outside by about two rows of cells, probably phloem, but not 

 showing any differentiation. Small protophloem elements, staining darkly, can 

 be seen upon the dorsal side of the bundle and an occasional similar cell can be 



Fig. 132. 



A. Two longitudinal sections of a somewhat older sporophyte of M. douglasii. 



B. Apical region of stem, showing apical cell and second leaf, /^ . X200. 



seen toward the ventral side, but most of the ventral surface is destitute of these. 

 The petiole broadens at its base, becoming flattened, and in this region the inner 

 phloem disappears and the bundle becomes collateral, as it is in Ophioglossum. The 

 tracheary tissue of the cotyledon in all of the Marattiaceae is composed of slender, 

 reticulately marked tracheids, like those of Ophioglossum. Sieve tubes are prob- 



