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 

 *j 7 . The spongy parenchyma is rather loose and consists 

 of slightly branching cells (Fig. 21, A, 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 



