IX 



A/ARA rriA CEJL—ISOETA CEjE 



287 



it does not extend entirely to the end. Its limits are clearly 

 defined from the periblem, in which the divisions are mainly 

 transverse and the cells arranged in regular rows. 



The primary xylem consists of small spiral and annular 

 tracheids at the base of the leaf, and from these the formation 

 of similar ones proceeds towards the tip. Their number is 

 small, even in the full-grown leaf, and they are the only 



t. 



Fig. 151. — Three successive horizontal sections of a somewhat advanced emhryo of /. echinospora 

 var. Braunii, X 260 ; R, root ; cot, cotyledon ; si, stem ; /, ligula. 



differentiated elements, the rest of the bundle showing only 

 elongated parenchyma, much like the original procambium 

 cells. 



The axis of growth of the primary root usually coincides 

 with that of the cotyledon, but this is not always the case. In 

 the very young root (Fig. 152, R) the end is covered with a 

 layer of cells continuous with the epidermis of the rest of the 



