289 



arenicola in a more natural place in the system, and I got 

 the idea, that this might be in the section Sisymhrina of 

 Arabis, and comparing the figure by W. Hooker with nume- 

 rous specimens of Arabis hiimifusa collected by J. Vahl, Th. 

 Fries, Kolderup R^senvinge and N. Hartz I became convinced 

 that this is its right place. I also found, that the only 

 difference between Eutrema arenicola and Arabis humifusa 

 was, that the first was figured with pods whose valves have 

 a very distinct and prominent middlevein, whilst the valves 

 of the latter are nearly nerveless. 



Last summer (1897) I had the opportunity of visiting 

 the Royal Herbarium at Kew and by the courtesy of the 

 keeper, Mr. J. G. Baker, I saw several critical plants; 

 among them the Parrya arenicola (Richards.) J. Hooker of 

 the Herb. Hooker, surely the plant, from which the figure 

 in W. Hooker: Flora Boreali-Americana is drawn; and it 

 was immidiately evident to me, that this plant is identical 

 with the Arabis humifusa^ the middlevein of the valves of 

 the original specimen being not more prominent than is 

 general in Arabis humifusa. On the other hand, when we 

 compare the two figures, that of W. Hookers (Flora Boreali- 

 Americana) and that of the Flora Danica we find some 

 difference, the first showing a plant with entire leaves (in 

 the description: integerrima vel parce dentata) and rather 

 short pods (in the description: pedicello vix duplo longiores), 

 the latter showing a plant with deeply dentate leaves (in 

 the description: grosse dentata) and long pods (in the de- 

 scription: pedicello triplo longiores). However these propor- 

 tions are variable. The common form has entire or slightly 

 dentate leaves, and the pods are generally three or four 

 times as long as the pedicels (Fig. 1). Richardson has found 

 the plant on sandy shores. In Greenland also the plant is 

 found on sandy ground. 



According to the rules of nomenclature the plant must 

 now be named Arabis arenicola, and the synonyms are 



Botanisk Tidsskrift. 21. Bind. 19 



