Rosaceæ. 29 



until the roots get somewhat older are the broad non-lignified 

 medullary rays developed. The periderm is not very thick; 

 in it one layer of cork-cells alternates with one layer of phel- 

 loid-cells. The older secondary cortex becomes highly com- 

 pressed and is somewhat collenchymatous. 



The rhizome, with the exception of the periderm, has a 

 structure similar to that in Pot. pulchella. In the periderm 

 one layer of phelloid-cells alternates with one layer of cork- 

 cells, as in the root. The inner cellulose-layer of the phelloid- 

 cells is fairly strong. An endodermis is present in the young 

 rhizome. The structure of the rhizome from Dauphiné, as 

 described by Hollstein, is similar to that of the present 

 one. HoLLSTEiN writes that the outermost layers of the 

 phloem is somewhat collenchymatous, and I find this gene- 

 rally to be the case in the greater part of the area between 

 the cambium and the phellogen, but the peculiar appear- 

 ance cannot be explained solely by this fact; it is no doubt 

 chiefly due to a strong radial pressure. 



The rhizome together with the primary root is the chief 

 depository for food-material ; and I find the alternation in the 

 abundance of starch and fat according to the season of the year 

 to be the same as is indicated in Pot. emarginata. The materials 

 contained in the rhizome in five different months from some- 

 what different localities in Greenland varied as follows : — 



18.11.92. 10. IV. 92. 31.V. 08. 1. VIII. 07. 4. XI. 91. 



Starch, a little. 0. to rather much, i much. 



0. 



Fat. much. | rather much. [ a little. very little. I rather much. 



The plants gathered in November, February and April 

 were from Danmarks in East Greenland, while the plants 

 gathered in May and August were from other localities in 

 East Greenland. The quantity of the starch increases during 

 summer till in August all the tissues are crowded ; in November 

 the starch has disappeared entirely; in February a small 



