Rosaceæ. 43 



Wolf is of opinion that, judging from its present distri- 

 bution, this plant is an old species which was probably origi- 

 nally circumpolar and has only recently advanced southwards 

 to about 40° N. lat. In Arctic and Subarctic regions it is 

 found both in the mountains and near the sea, in southern 

 regions (Europe and western Asia) only in Alpine and Sub- 

 alpine mountain regions. 



It grows on rocks, on heaths on grassy slopes and in copses. 



The shoot-structure is monopodial and caespitose, but 

 the tuft is rather loose in form, and ascending or almost 

 horizontal branches, 10 — 15 cm. in length, commonly occur. 

 There is some individualization of the older branches. The 

 branches are for many years covered with the remains of 

 brown leaf-sheaths. 



Sylvén writes that in Sweden Pot. maculata is evergreen 

 even in mountainous regions and in the Copenhagen her- 

 barium there are specimens with green leaves from Disco in 

 Greenland gathered in September and in the beginning of 

 April. In a garden in Copenhagen it remains green through 

 the winter. 



Anatomy. My material of Pot. maculata was extremely 

 poor with regard to roots ; but it appeared that the exodermis 

 of the absorbent roots has thin walls very much as in Pot. 

 Anserina. The epidermis of the absorbent roots proved to 

 have collapsed. No mycorrhiza was seen. 



The structure of the rhizome resembles in its main 

 points that of Pot. pulchella (see Fig. 9, G), the medullary 

 rays are however fewer in number — about 4. Fairly distinct 

 annual rings were seen in the wood. A shoot, 7 cm. long, 

 was about 6 years old, and another which measured about 

 3 cm. was of the same age. The pith in these shoots was 

 still alive. The secondary cortex had somewhat thickened 

 walls and its outermost part was found to be somewhat com- 

 pressed. The periderm is thick, there are about 6 layers of 



