286 



6. Porphi/rion. 



Saxifraga oppositifolia L. iFigs. 28 and 29 1. 



Saxifraga oppositifolia L. extends lo the highest summits 

 of the mountains into the snow-flora (Norman, Warming). Grows 

 on dry. stony ground, upon the rock itself or among large 

 boulders. Consequently it is a xerophyte. and shows this 

 very distinctly in its internal structure. The leaf has only one 

 hydathode at the apex. The marginal hairs are irregularly 

 multicellular. 



The upper epidermis (Fig. 29i has fairly straight lateral walls, 

 with numerous pits. The outer walls differ in thickness in the 

 different parts of the leaf: towards the apex they are very 

 thick, and from thence become gradually thinner towards the 

 leaf-base. The cuticle is distinct and very finely wrinkled. The 

 stomata. with fair regularity, are placed parallel to the length 

 of the leaf, only a few depart somewhat from this position. 

 Their distribution upon the leaf-blade is very remarkable. They 

 are entirely absent from the extreme tip of the apex, upon 

 which is the hydathode. Immediately behind the apex they 

 occur in a broad band across the leaf and are partially con- 

 tinued along the under-side of the leaf-margin. 



The epidermis of the lower surface iFig. 29i closely resembles 

 that of the upper; its cells, however, are somewhat more elongated 

 longitudinally. The distribution of the stomata is like that upon 

 the upper side. 



The palisade-cells of the leaves (Fig. 28i, at the exposed apex, 

 are very distinct and occur both upon the upper and lower surface, 

 the leaf being directed sharply upwards. Further down towards 

 the base the differentiation between palisade-tissue and spongy 

 parenchyma disappears entirely. The spongy parenchyma con- 

 sists of rounded, unbranched cells, fairly compact; within the 

 epidermis towards the leaf-base there is a single layer of cells 

 which is quite without intercellular spaces. As already men- 



XXXVI. 19 



