Rosaceæ. 



101 



respectively. In Iceland Jonsson (1. с.) found no flower- 

 buds on March 26, but, as Fig. 38, A shows, young inflores- 

 cences are at any rate to be found in Greenland in August. 

 Anatomy. The adventitious roots are triarch-tetrarch. 

 The central cylinder is surrounded by a suberized endodermis. 

 The outer wall of the epidermis, especially in A. alpina, is some- 

 what thick {2.b ju), but the skin is functional for a certain 

 period only, after which it is thrown off; this is due to a struc- 

 tural feature which is shown in Fig. 38, В and which was 

 especially pronounced in A. færøensis. The exodermis consists of 

 large cells, the thin radial walls of which are ruptured sooner 



Fig. 38. 



AlcMmilla alpina: A, Longitudinal section through a young bud containing 

 the primordium of an inflorescence (Greenland; 1. 8. 1885; Veo)- C, Portion 

 of a transverse section through the periderm of a rhizome (Greenland ; 

 '"/i); k< layer of cork; p, phelloid-cells. — AlcMmilla færøensis : В, Portion 

 of a transverse section of a young adventitious root of the first order ; 

 Ip, epidermis ("7i)- 



or later, and the following layer of the cortex which has 

 fairly thick walls and gradually becomes corky, functions 

 then as epidermis till the periderm is formed. The primary 

 epidermis is thrown off before the root in the zone in question 

 has begun its secondary growth in thickness. 



In the primary cortex in the roots of A. alpina fungal 

 hyphæ have been found. 



Periderm is probably formed in the pericycle; it is not 

 developed until a continuous woody portion is produced in 

 the central cylinder; it consists of alternating series of layers 

 of 1 — 3 layers of cork-cells and phelloid-cells; it contains 

 rather large intercellular spaces which are however often absent 



