Scrophulariaceae. 403 



of short palisade-cells, with rather large intercellular spaces; 

 the spongy parenchyma consists of only slightly branched 

 cells. The mesophyll of the upper leaves of the stem (i. e. 

 the leaves subtending the flowers) appears, on the whole, 

 to be more lacunose in structure than that illustrated in 

 Fig. 14, С 



The margins of the teeth of the leaves are somewhat 

 bent over, whereby a concavity is produced on their under 

 side. In this concavity the leaf-surface is densely covered 

 with glandular hairs, and the cells of the epidermis differ in 

 character from the other epidermal cells of the leaf. For 

 whilst these, both on the upper and lower surface — and 

 especially on the upper side of the teeth of the leaves — 

 have strongly undulating lateral walls (Fig. 14, A and B), 

 which only here and there show a small flanged thickening, 

 the epidermal cells in the concavities, and especially those 

 which bear the glandular hairs, have straight or only slightly 

 wavy lateral walls (Fig. 14, D and E), which are often (not, 

 however, in the places illustrated in Fig. 14, D) furnished 

 with flanged thickenings, the one by the side of the other. 

 Stomata are almost equally abundant on both leaf-surfaces, 

 in the concavities of the lower side of the teeth, however, 

 they are less frequent; the guard-cells are on a level with 

 the surface. In the teeth the veins break up into a fine net- 

 work of tracheids. 



The glandular hairs which occur on the lower side of 

 the teeth are of two types: (1) a smaller one with one-celled 

 stalk and two-celled, globular head, and (2) a larger one with 

 two or more frequently four-celled cupola-shaped head, seated 

 upon a short and broad stalk-cell which partly sinks below 

 the leaf surface, the inner-wall of the stalk-cell, during the 

 development of the hair, becoming rounded inwards, thus 

 pressing the layer of epidermal cells, situated under the stalk- 



