EPIDERMIS. 



85 



aggregated wax-covering, since it consists of an aggregation of very delicate rods or 

 granules, which cover the cuticle not with a simple layer, but with several irregular layers. 

 Examples of the aggregated rods are found on the white Eucalypti (E. globulus, pul- 

 verulenta), Acacias (A. Hiigelii, cultriformis), Lonicera implexa Ait., Andromeda 

 dealbata ; Secale cereale, Elymus arenarius, Encephalartos horridus ; examples of 

 aggregated granules are found on Kleinia ficoides, Ricinus communis, under surface 

 of the leaf of Abies pectinata and its allies. Intermediate forms between the third 

 and fourth type are sometimes found, e. g. leaves of Agave Americana. 



The wax-coverings usually cover the whole epidermal surface evenly, or with 

 the differences of form described above for the epidermal cells of differing contour. 

 The granular and aggregated coverings also overlie the guard-cells of the stomata 

 up to the entry of the slit. The stratified coverings, where observed, leave the stomata 

 free, in so far as they belong to parts already unfolded, or at least they become so thin 

 as to be unrecognisable over the guard-cells. On the other hand the wax-layer of the 

 young not yet unfolded leaf of the Carnauba palm completely covers the stomata also : 



B 



Fig. 39.— Strelitzia ovata. A under surface of a leaf still in course of unfolding; on the epidermal cells are rods of wax in 

 course of growth ; surrounding the stoma is the striated ring —B transverse section of a mature leaf. Epidermis with one stoma 

 (lying above the wide respiratory cavity S), the rods and the ring. Under the epideirois is the large-celled hypodermal layer ; 

 below this the chlorophyll.containing cells of the leaf parenchyma {375). 



these however are freed when the leaves unfold, since the spontaneous crumbling 

 off of the wax-layer on the unfolded leaf, though not indeed directly observed, may 

 still be certainly assumed from the data at our disposal. Certain of the Scitaminese 

 show remarkable peculiarities in the distribution of the rods. On the leaf of INIusa 

 ornata the short rods are situated chiefly, if not exclusively on the edges of the 

 epidermal cells. Strelitzia ovata (Fig. 29) has rods distributed over the whole lower 

 leaf-surface. Those which stand on the annular rows of cells surrounding a 

 stoma converge with their hooked ends towards the stoma, and on the edge of 

 the wall, which separates the two half-moon-shaped subsidiary cells from the 

 surrounding epidermal cells, stands a ridge consisting of wax, and having the form 

 of a ring diminishing conically outwards, with its margin curved inwards, and with 

 radial striation, which gives it the appearance of being composed of many con- 

 verging crosiers. The outer surface of the subsidiary cells themselves, and of the 



