EPIDERMIS. 91 



On those parts which have a glandular surface only in their younger stage, as 

 Rumex, Betula, &c., the epidermal cells of the glandular surfaces are not distinguished 

 by peculiarities of structure. On the sticky zones of the Sileneae between the ordinary 

 epidermal cells there are others, which are characterised by special form and dark 

 granular contents, to which alone Unger attributes the excretion of the glutinous 

 substance. In Silene nemoralis^ these are simple, broader cells, slightly curved 

 outwards like papillae : in Lychnis viscaria ^ they are very short hairs consisting of one 

 small pedicel cell, and one roundish apical cell which rises only slightly above the 

 epidermal surface. 



These circumscribed glandular areas have the common peculiarity, that their 

 epidermal cells are richer in granular protoplasm, smaller, and more delicate than 

 those on the rest of the dermal surface, and are of the form of elongated prismatic 

 or narrow pyram.idal bodies with the longer axis standing perpendicular to the surface. 

 In Passiflora spec, the prismatic cells are divided by a transverse wall into two 

 nearly equal halves : the glandular epidermis thus consists of two layers. In Clero- 

 dendron fragrans also there are two layers, the inner consisting of angular tabular 

 cells with very thick lateral walls, and the outer of narrow prismatic cells, which are 

 at least sixteen times as numerous. It is obvious at first sight that in all cases the 

 narrow prismatic cells result from repeated division of the primary epidermal elements, 

 and that the structures in question are morphologically allied to the scale-like hair- 

 structures. In fact there exists between the glandular area of Clerodendron fragrans, 

 and a group of the laterally united top-shaped scales of Hippuris or Catalpa, only 

 this one important difference, that the latter are placed above, the former in the 

 epidermis. The glandular area on the leaf-tooth of Mercurialis annua may, as regards 

 its form and articulation, be also termed a top-shaped scale, &c. 



b. The intramural glands, in which the product of secretion appears in the 

 limiting wall between the cells, are obviously always multicellular. They rise as 

 scales, capitate hairs, or villi above the outer surface, or they do not rise above it, but 

 rather intrude as depressed glands into the subepidermal tissue. The connection with 

 the bladder-like forms is effected by the villi of buds found by Hanstein in many 

 plants, in which the resinous secretory layer appears both under the cuticle of the 

 outer surface, which is raised like a bladder, and on the limiting surfaces of the lateral 

 and inner cellulose walls (Azalea indica, /. c, Figs. 93-95). In the typical allied forms 

 no secretion occurs between the outer wall and cuticle, but only on the limiting sur- 

 faces of the division walls. The latter are finally separated by a voluminous secretory 

 layer. The cells, which in the known cases are narrow and elongated, stand in the 

 secretory mass like the rods of a trellis or the pillars of a vault. 



Of the allied hair-structures, which protrude outwards, may be named the large 

 capitate glandular hairs of Ledum palustre : the flat top-shaped glandular scales of 

 the under surface of the leaf of Rhododendron fermgineum, hirsutum (Fig. 41), 

 Caucasicum. Further investigation will probably increase the number of examples 

 of this class. Those bodies which appear to the naked eye as bright round points 

 on both surfaces of the leaf of many species of Psoralea (Fig. 42; e. g. P. bituminosa. 



Unger, Grundlinien, p. 8i. ^ Idem, Anat. und Physiol, p. 214. 



