HOLLY LEAF 131 



Cat transverse sections of the petiole of the Holly : 

 mount in glycerine, and note in the slightly oval section 

 under a low power the epidermis, and broad band of 

 cortex : also the large, semilunar vascular bundle 

 which occupies a central position, and has its xylem 

 disposed at the concave side, nearer to the upper surface, 

 and its phloem disposed at the convex side, which is 

 directed towards the lower surface of the petiole. 

 One or two small outlying bundles are also to be 

 seen. 



Note that there is a cambium-layer, which shows signs 

 of activity, between the xylem and phloem of the large 

 bundle. 



TV. Transverse sections of 'the lamina of the Holly 

 may be prepared as above directed for the Sunflower, 

 and be mounted in dilute glycerine, others in chlor-zinc- 

 iodine. Starting from the upper surface of the thin 

 lateral portion of the lamina, observe successively the 

 following tissues : 



1. Epidermis, a single even layer of cells, with thick 

 walls, and colourless protoplasmic contents ; no hairs or 

 stomata are to be seen ; the lateral walls are pitted : 

 note in sections treated with chlor-zinc-iodine that the 

 outer wall, which is thicker than the rest, is differentiated 

 into 



a. Cuticle, a continuous, well-defined and highly- 

 refractive layer, covering the whole epidermis externally : 

 this stains yellow with chlor-zinc-iodine. 



b. Cuticularized layers, of granular appearance, 

 and stained a deeper colour than (a) with chlor-zinc- 

 iodine: they are intermediate in properties between 

 cuticle and true cellulose. 



K 2 



