102 Knud Jessen. 



from the inner side of the cork-layers. The phelloid-cells 

 contain starch-grains which are found especially along the 

 inner walls. The periderm may constitute as much as I of 

 the radius of the root. Medullary rays are absent from the 

 wood. There are distinct annual rings; the oldest roots I 

 have seen were 5 years. 



The central cylinder in the rhizome is surrounded by 

 a distinct endodermis. The primary bundles are considerable 

 in number and are more or less confluent. The pith which 

 is of simple parenchyma lives in A. alpina as long as the shoot, 

 but in A. færøensis it apparently dies at an earlier period. In 

 the latter species the pith constitutes a larger portion of the 

 diameter of the shoot than in the former; it is the chief reser- 

 voir of food-material and in the autumn is found crowded 

 with starch. Rhizomes of A. alpina collected in Iceland in 

 March contained, on the other hand, almost no starch, and 

 shoots of both species collected in the Botanic Garden in 

 Copenhagen on Jan. 5 contained only a small quantity; on 

 the other hand, they contained large quantities of fat. 



In the first period of vegetation of the shoot a continuous 

 cambium produces a small quantity of wood. Medullary 

 rays are absent from the latter (cf. Hollstein who has stu- 

 died A. alpina). In A. alpina the diameter of the vessels 

 was larger in specimens from Copenhagen than in those 

 from more northern regions. 



The periderm is formed by the division of the outermost 

 layer of the pericycle and is developed even in the first period 

 of vegetation of the shoot. 2 — 3 layers of phelloid-cells 

 alternate with one layer of cork-cells. But in the Botanic 

 Garden in Copenhagen the periderm in these two species 

 contained only scattered cork-cells; in such plants it func- 

 tions almost solely as a depository of food-material while 

 the protective layer proper consists of dead masses of leaf- 

 sheaths, primary cortex and the older layer of the periderm. 



