388 



steril may siil)teii(l a shoot with eloti^^ated iiiteriiodes, which 

 continues Ihe iiiaiii axis sympodially until that also produces 

 a flower, and so on. Hut in Greenland and Iceland, judging 

 Ironi herbarinin-material, it seems probable that rarely more 

 than two generations of axes attain the flowering stage. In the 

 other axillary-shoots of the stem the inlernodes either remain 

 short or the axillary shoots develop like the parent-axis and 

 flower; their axillary shoots are rosettes; this is also frequently 

 the case with the main shoot. 



The more vigorous shoots occur in the lower axils of the 

 straight stem, and from their bases and from the nodes of the 

 parent-axis vigorous adventitious roots arise late in sum- 

 mer. They are of two kinds: some slender, hyaline and abun- 

 dantly branching, and others wiiich are white and almost un- 

 branched and begin with a somewhat thickened base, becoming 

 thinner downwards; these roots may be regarded as storehouses 

 of food-material for the axillary-shoots which become inde- 

 pendent during autumn by the death of the parent-axis. 



The flower has five somewhat prominent pe rigone-le aves 

 and five yellow nectary-leaves which do not overlap and 

 are somewhat longer than the perigone-leaves (from 2b to 

 6 mm.). The nectar,! es are simple and pocket-shaped (Fig. 33). 

 The anthers are turned sideways. The cluster of 

 ovaries is almost globular and does not overtop the 

 stamens. In the material, both from Greenland and 

 Denmark, the flowers were somewhat protandrous- 

 homogamous. The diameter of the flower in 

 Arctic Norway is about 9 mm. (Norman), in Green- 

 R.reptans. laod and in Denmark about 5 mm. The time of 

 (Gree^Indf«/!). floweriug in Arctic Norway is from the middle of 

 July to September, and in Denmark from the middle of June 

 to the middle of September. 



The ripe fruits have a more or less curved beak, and 

 if they are not wetted, can float for a long time (from one to 



Fig. 33. 



