94 PKACTICAL BOTANY. 



to have been cut transversely, obliquely, or longitu- 

 dinally. 



5. A second layer of epidermis bounds the section 

 on the lower side ; it has the same characters as the 

 upper layer, but stomata are more frequent. Note the 

 large respiratory cavity, and two small guard cells. 



Hairs as before seen on the upper surface. 



Note the mucilaginous walls of these hairs. 



Since the leaf of Heliantlius is not a universal 

 type, it would be well to study also the structure of 

 other types, for instance the coriaceous leaves of the 

 Cherry Laurel (Prunus Lauro-Cerasus), and the cylin- 

 drical leaves of the Stonecrop (Sedum acre). 



Special structural peculiarities are to be observed in the leaves 

 of other plants ; for instance, an epidermis consisting of more 

 than a single layer of cells, e.g. in leaves of Ficus, Piperacece, 

 Begoniacem, &c. ; Cystoliths in the cells of the epidermis, e.g. 

 FicuSj Urtica, &c. ; glandular structures, e.g. in Ruta, Psoralea, 

 &c., &c. 



III. Taking that of the Cherry Laurel sections 

 maybe prepared as above directed for the Sunflower, 

 and be mounted in dilute glycerine. Starting from 

 the upper surface, 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 ; 

 the outer wall is differentiated into 



a. Cuticle, a continuous, well-defined layer, covering 

 the whole epidermis externally. 



