134 PEACTICAL BOTANY 



explained by the granular cuticularized layers observed 

 in transverse sections ; the lateral walls are pitted, the 

 contents colourless, and there are no stomata. 



The cells of the lower epidermis are similar to the 

 above; but stomata are numerous; they have no 

 definite arrangement. Note the two sausage-shaped 

 nucleated guard-cells, inclosing the pore ; they contain 

 chlorophyll, and are slightly depressed below the general 

 surface. 



VI. Cut transverse sections of the cartilaginous 

 margin of the leaf of the Holly, and observe the same 

 structure as before ; but towards the rounded margin 

 the hypoderma increases in thickness to two or more 

 layers, and at the extreme margin a large mass of 

 sclerenchyma lies immediately below it : the cells have 

 thick stratified and pitted walls : they give the reactions 

 of lignified walls but not distinctly or readily. This 

 tissue is of importance, as giving strength and rigidity 

 to the leaf. 



N.B. The Cherry Laurel (Prunus Lauro-Cerasus) 

 may be used instead of the Holly, the structure being 

 very similar, with the exception that the hypoderma 

 and marginal sclerenchyma are absent. 



ii. Isobilateral Type. 



For comparison with the above, which is by far the 

 commonest type, examine the laterally compressed 

 petiole (phyllode) of some one of the phyllodineous 

 Acacias, e.g. A. armata or A. hderophylla : observe in 

 the latter species that the petiole of some leaves which 



