Scrophulariaceae. 397 



In the wood, medullary rays are entirely wanting (the 

 radiating lines in Fig. 12, A, В and С indicate only the radial 

 arrangement of the elements); exteriorly, the ring of wood 

 consists chiefly of wood-fibres ; interiorly, vessels become more 

 frequent, and are accompanied by partly lignified paren- 

 chyma. In the basal portion of the stem the vessels are 

 relatively more numerous than shown in Fig. 12, Z), and the 

 cells of the stereom are thinner-walled. The pith consists 

 exteriorly of lignified, rather thick-walled, distinctly poröse, 

 axially elongated parenchymatous cells, towards the centre 

 the cells of the pith are thinner- walled, non-lignified and 

 die away, so that the stem becomes hollow. 



The Leaf: Any difference as regards anatomy could 

 scarcely be demonstrated in the leaf-types of the different 

 forms. Transverse sections, slightly magnified, of the leaf of 

 var. septentrionale and of the principal form are shown in 

 Fig. 13, A and Б, the three main veins and the numerous 

 fine anastomoses are seen. 



The vascular bundle of the main veins has on its under- 

 side a covering of somewhat collenchymatously thickened 

 elements; on the upper side the surface of the lamina dips 

 down towards the vascular bundle. The structure of the 

 mesophyll is fairly homogeneous, thus in Fig. 13, F it is 

 hardly possible to demonstrate a palisade-layer ; in specimens 

 from Kola the uppermost layer of the mesophyll was how- 

 ever elongated in a somewhat palisade-like manner. Chloro- 

 phyll-grains occurred abundantly in the entire mesophyll, 

 and besides this they were found in the epidermal cells of 

 both surfaces. 



The epidermal cells of the upper surface have from 



straight to shghtly undulating lateral walls, those of the lower 



surface can be more strongly undulating. Both the outer 



and lateral walls of the epidermal cells are thin; the cuticle 



ХХХЛШ. - 26 



