18 Knud Jessen. 



ing of larger cells of which a greater or smaller number 

 often dies, but nevertheless the shoot cannot be called hollow. 



The leathery leaf, which is 238—270 a thick, has a deci- 

 dedly xeromorphic structure in correlation with the fact 

 that the plant grows in dry localities ; perhaps it also 

 may live through the winter. It is glabrous upon the upper 

 surface, but upon the lower surface it bears in addition to 

 scattered adpressed hairs of the common type also numerous 

 glandular hairs of two other forms (Fig. 6, E, F.). In the 

 smaller form the apical cell is almost spherical and in the 

 larger ovate to cylindrical. The stalk is often several-celled. 

 These hairs spring from epidermal cells which are smaller 

 than the rest and have a thin outer wall. Perhaps these 

 hairs with their thin-walled and plasma-filled apical cells 

 are able to absorb water which may then be carried into 

 the leaf. Both the upper and lower epidermis have very 

 strong outer walls; thus that of the upper surface measured 

 between 8 and 11 fi and that of the lower about 11^. The 

 lower surface of the leaf is moreover highly reticulated. The 

 lower epidermis in particular has a strong cuticle which is 

 somewhat rough. The epidermis of the upper surface is 

 characterized by its tangential walls being mucilaginous to 

 a very high degree, especially the inner; the mucilaginous 

 covering is always wanting above the larger bundles. (Fig. 

 6, A.). Both leaf-surfaces bear stomata, but upon the upper 

 surface they are very scattered and are surrounded by a 

 group of smaller cells (Fig. 6, B). Upon the lower surface 

 they are placed closely and are not definitely arranged. They 

 are sunk below the level of the surface (Fig. 6, A). The 

 radial walls on both the upper and lower surface are only 

 slightly wavy; they are highly perforated on the lower sur- 

 face (Fig. 6, C)\ on the upper surface the pores occur in larger 

 quantities only near the bundles. 



The palisade parenchyma occurs in 2 — 3 layers of closely 



