8o PRACTICAL BOTANY 



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. 



IV. 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. Cuticuiarized layers, of granular appearance, and stained 

 a deeper colour than (a) with chlor-zinc-iodine : they are inter- 

 mediate in properties between cuticle and true cellulose. 



c. The cellulose-layer, which abuts on the cavities of the 

 cells ; this stains blue with chlor-zinc-iodine. 



2. Hypoderma, a strengthening tissue, which is immediately 

 below the epidermis, and consists of a single layer of cells : at 

 the midrib it may widen into two layers : the walls are pitted, 

 and stain bluish with chlor-zinc-iodine. 



3. The palisade-parenchyma, composed of thin- walled, oblong, 

 closely-packed cells, with their longer axes perpendicular to the 

 surface of the leaf ; the cells are somewhat irregularly arranged 

 in three layers ; observe nuclei and chlorophyll-grains ; here 

 and there are cells (idioblasts) with but little protoplasm, in 

 which is inclosed a large crystal. Passing towards the lower 

 surface of the leaf, this tissue merges gradually into 



