378 



PRIMARV ARRANGEMENT OF TISSUES. 



vertically to the surface under each epidermal furrow, ending some distance within 

 the latter in a conical or hollow-conical expansion. Upon or in this expansion rests 

 an epithema, of oval or elongated form according to the species, and extending to 

 the epidermis, which contains water-pores. Its cells are on the average about one 

 fifth the size of those of the surrounding chlorophyll-parenchyma, they are roundish or 

 slightly elongated in the same direction as the vascular elements, with watery, colour- 

 less contents. They are almost uninterruptedly united with each other, and even the 

 cavities below the water'-stomata are small. In the furrows of the leaf of the Saxifrages 

 mentioned above, the end of the vascular bundle is expanded into a large epithema 

 of an approximately conical form, with its base resting on the epidermis of the furrow. 

 Its structure is very similar to that of Crassula, its cells are elongated in the same 

 direction as the tracheae, and the whole body, like the vascular bundles themselves, 

 is ensheathed by a layer of cells which are very rich in tannin. The epithemata in 



FIG. iSo.— Crassula arborescens. Longitudinal section, vertical to the leaf-surface, through the apex of a leaf. 

 Magnified 30—40. e—e' epidermis ; ^vascular bundle, divided into two branches, which terminate below a small- 

 celled epithema in broadly conical ends consisting of short tracheides ; the branch at/ on the upper, that at/' 

 on the lower surface of the leaf. 



the furrows of Ficus have an approximately discoid general form, are round-celled, 

 and in other respects are also similar in structure to those of Crassula. The same 

 also holds good in general of those epithemata which lie below the glandular 

 portions of the epidermis. How far the nature of the contents of their cells shows 

 remarkable peculiarities, still remains to be more exactly investigated. 



Sect. na. In the leaves of the Conifer ce, as stated above, the finer ramifications 

 of the bundles are absent ; the leaves are traversed either by a number of bundles 

 of approximately equal thickness, or in most cases by a single median one ; in 

 most Abietinese by a median pair of bundles running close side by side, only, 

 separated from one another by one or two layers of elongated cells (e. g. Abies 

 excelsa, pectinata, Pinsapo ; Cedrus Libani ; Pinus Pinaster, Laricio), or by a thick 

 strand of sclerenchymatous fibres. The bundles are collateral, and their orientation is 



