Rosaceæ. 15 



certainly able to float. This point has been discussed by 

 KøLPiN Ravn (1. с.) among others. He found that the fruits 

 keep afloat even while they are germinating, and anatomical 

 investigation showed that the thick testa consists of several 

 layers of cells, which contain air. The inner part of the peri- 

 carp consists of protective stone-cells. 



Potentilla tridentata Soland. 



Lit. Hartz, 1894; Wolf, 1908. 



This plant grows in Greenland, Arctic North America, 

 Labrador, Newfoundland and Canada. It occurs in clefts 

 of rocks, on lichen-heaths and in other dry localities. 



The alcohol material was collected in the following loca- 

 lities in Greenland: Christianshaab, Ivigtut, Sukkertoppen 

 and Holstensborg. 



Lange and Wolf call Pot. tridentata an undershrub, 

 and as is the case in Potentilla palustris the lignified axis 

 lives several years. It is a typical wandering plant with 

 a horizontal, richly branched rhizome from which slender 

 adventitious roots arise. Usually the runners, which may 

 be above 30 cm. long, are etiolated and bear scale-leaves, 

 but creeping shoots with elongated internodes, bearing only 

 foliage-leaves, are also met with; such epiterranean shoots 

 may also be ascending. The scale-leaves are distichous. 

 The shoots which arise from the runners and which often 

 grow out from older stems have probably a life-cycle of several 

 years. In the first period of vegetation they are wandering 

 and pass the winter with straight apex, and not until the 

 second period or perhaps even later do they enter the rosette- 

 stage and form foliage-leaves. It appears to be necessary 

 for the young rosettes to pass through a stage of vegetative 

 growth before they attain the flowering stage. The apex 

 of the rosette-shoot is protected during winter by the large, 

 closely folding sheaths of the older leaves; scale-leaves are 



