Rosaceæ. 103 



Fig. 38, С shows а transverse section of the periderm of 

 A.alpina; it contains large intercellular spaces. During summer 

 the starch-grains are found especially along the inner walls 

 of the phelloid-cells; in the autumn the cells are entirely 

 filled by them. 



The primary cortex is ruptured owing to secondary 

 formations, but even in the second summer it may be found 

 alive. Bast does not occur. 



The structure of the floral-shoot is very much like 

 that described by Hollstein from the Dauphiné-Alps. A 

 collenchyma, 1 — 2 layers thick, occurs, and within the endo- 

 dermis 2 — 3 layers of bast unite with the secondary wood, 

 which consists of several-layered strong-walled tracheids, so 

 that the groups of sieve-tissue are entirely surrounded by 

 stereom. The pith dies away in the centre. 



The leaves are from 200 to 220 /i thick, and generally 

 somewhat thicker in A. alpina than in A. jærøensis. The 

 epidermis of the upper surface is glabrous in the former and 

 slightly hairy in the latter; it is high, and the outer wall in 

 A. alpina is about 6^ and in A. jærøensis 4 — Ъ p. thick, while 

 the outer wall in the epidermis of the lower surface is about 

 3.3/^ and about 2p thick respectively, Stomata serving as 

 respiratory organs are absent from the upper surface. The 

 lower surface is densely hairy and here the stomata occur 

 abundantly and are somewhat sunk below the level of the 

 surface (Fig. 39, B). Knothe (1. c.) illustrates by a figure 

 of A. alpina how the hairs are appressed upon the lower 

 surface of the leaf, and he states that this is not wetted. 

 The palisade parenchyma consists of a well-marked layer 

 which constitutes about one-half of the thickness of the 

 mesophyll. The proportion between the leaf-thickness and 

 the thickness of the palisade tissue is in A. alpina about 

 ^ and in A. jærøensis about —• The intercellular spaces 

 in the spongy parenchyma are not large, but sections 



