136 Carsten Olsen. 



stand so very close to each other, it is more hkely they 

 could reach the nearest ones and deposit pollen on their 

 stigmas, and, as a matter of fact, I have seen the anthers 

 of neighbouring flowers in close proximity to a flowers 

 stigma". 



Warming found the same form of development in arctic 

 Norway (Tromsø, Alten) and pure homogamy was only 

 found once. The pollination takes place by insects, which 

 are guided to the flowers by the four big and petal-like 

 involucrals; according to Willis and Burkill the visitors 

 are few, mainly of the order of Diptera. 



The pollen grains, which are only few in number, 

 have three strongly projecting pores (fig. 2). 



Deformity of the inflorenscence is not quite uncommon; 

 sometimes the involucral is partly and even completely 

 green. Warming mentions such deformities in his notes 

 from "Sukkertoppen"; in the same locality he found spec- 

 imens with 6 or 7 involucral leaves. 



The fruit is a drupe; the stone is two-celled, one of 

 which nearly always remains barren; the ripe fruits, red in 

 colour, are found in Greenland in August and September. 

 The dispersal takes place by animals (Hesselman found 

 40 stones in the excrements of a Larus marinus), and 

 partly by means of water; the plant often grows near water- 

 courses, and the stones being lighter than water, will often 

 be carried far away; Sernander found them thrown up by 

 the sea near a small island in the Baltic, more than 400 km 

 from its nearest habitat. 



Anatomy. 



The leaf is dorsiventral, with a pallissade tissue of 

 one layer of cells and a pronounced spongy tissue (fig. 4). 

 The epidermis of the upper surface consists of very large 

 cells, while those of the epidermis of the lower surface arc 



