TRITICUM 



167 



Anatomy of the Leaves — the Coleoptile. — The coleoptile, 

 or second leaf, consists of a parenchymatous cylinder, limited out- 

 wardly and inwardly by epidermal tissue, through which two 

 vascular bundles extend. The thin-walled cells of the outer 

 epidermis are elongated, and there are one or two rows of stomata, 

 lying parallel to the vascular strands, that pass from the base 

 to approximately the tip of the leaf where the stomata are more 



chl par 







Fig. 75. Transection of a small portion of the coleoptile including the vascular bundle and 

 surrounding tissue: c^/ /»^r, chlorenchyma ; /;A, phloem; xy, xylem. (After Avery.) 



numerous. No hairs are developed on either epidermis, and the 

 inner one has no stomata. The parenchymatous cells abutting 

 the outer epidermis and the cells surrounding the vascular bundles 

 contain chloroplasts. (Fig. 75.) The vascular bundles are col- 

 lateral; and, as compared with the stem bundles, have relatively 

 more phloem than xylem. 



The Prophylls. — The structure of the prophyll is not unlike 

 that of the coleoptile. The rectangular epidermal cells are elon- 

 gated and there are unicellular hairs along the margins of the 

 flat surface of the prophyll. At its apex, longitudinal rows of 



