Rosaceæ, 53 



The palisade parenchyma consists of 2 — 3 layers of cells, of 

 which the two upper layers are fairly well-marked. The 

 proportion between the thickness of the leaves from Green- 

 land and the thickness of the palisade parenchyma is about 

 Y- The spongy parenchyma is rather loose and consists 

 of slightly branching cells (Fig. 21, ^, E). 



It is normal for the yellow flowers to occur singly on 

 the often long flower-stalks. Wolf records the diameter of 

 the flower as 18 — 20 mm., and Knuth as 20 mm. 



The flowering period occurs in Arctic Norway between 

 June 25 and Sept. 21 (Norman), Lange records as regards 

 Greenland July — August; in Central Europe the flowering 

 begins in May. 



My material contained flowers from different localities 

 in Greenland, and those which had not entered the homo- 

 gamous stage showed a somewhat considerable degree of 

 proterogyny. Anthers in fully expanded young flowers were 

 still closed while the stigmas were found to be highly papil- 

 lose even before the petals had opened. It was, however, 

 impossible to find a single pollen-grain on these highly papil- 

 lose stigmas, but, as soon as the anthers had opened the 

 stigmas were found to be densely covered with pollen. This 

 fact does not seem to indicate that insect-invisitors have 

 been frequent. The stamens are longer than the styles; 

 they are erect or somewhat bent inwards when the anthers 

 are open. Self-pollination is consequently possible, which 

 opinion is also maintained by Knuth. In the Friesian Islands 

 he found Pot. anserina to be purely homogamous, and he writes 

 that spontaneous self-pollination must take place as soon as 

 the pollen-grains no longer adhere to the drying pollen-sac; 

 he found that there was a possibility for insect-pollination 

 in the fact that at first the pollen was rather firmly attached 

 to the open pollen sacs. According to Knuth in inclement 

 weather the flowers are half-closed during the day and entirely 



