DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 315 



this plant, in which state it differs in no respect from pratensis. I have not seen tlie 

 fruit, however. 



C. umbrosa, DC, is referred by Pries to a variety of amara, L. ; both are Lapponian. 



EuTEEMA arenicola. Hook. I have examined this plant very carefully ; it is certainly 

 not a JEutrema. In the few specimens known to me the radicle is slightly oblique. 

 Turczaninoif (in Herb. Hook.) suspects that it may be his E. piliferum {Braba grancli- 

 fiora, C. A. M. ; Fachyneurtmi grandijlorum, Bunge ; Braya 3Ieyerl, Bge. ; Barrya mi- 

 crocarpa, Led.) ; but I find no traces of the peculiar hairs of this plant in the P. arenicola. 

 Richardson observes that it ranges from 107°-150° W. I have seen no specimens but his 

 own. 



Vesicaria arctica. Rich. Planchon , who has examined the specimens in the Hookerian 

 Herbarium with a great deal of care, confirms the identification of the Chilian plant with 

 the arctic. It is singular that this plant should be found as far north as 81° in Green- 

 land, but not amongst the Polar American Islands. 



Draba. Of all the arctic genera, none but Salix present so many diflS.culties as Braba. 

 Whether by variation, or hybridization, or other unknown cause, the prevalent forms seem, 

 wherever they grow, to pass into one another by insensible gradations ; and no botanist 

 has succeeded in bringing the arctic stunted varieties within such specific limits as to have 

 gained the assent of others. No doubt many are, in their arrested condition of growth, 

 absolutely undistinguishable in the present state of science ; and whoever attempts their 

 discrimination must expect to change his opinion somewhat at every re-examination. I 

 am fortunate in having Mr. Ball's advice upon some of the European species, which he 

 has studied with great care, and have followed his opinion in the naming and grouping 

 the arctic ones ; unfortunately, however, he has not completed his study of the genus, 

 nor of all the species here enumerated ; so that the geographical data are approximate 

 only ; nor does he speak with implicit confidence of their synonymy. In addition to the 

 excellent critical notes he has published in the Bulletin of the Botanical Society of Paris 

 (vol. vii. pp. 227 & 247), I have from him the following provisional grouping of the com- 

 moner forms : — 



1. B. androsacea, Wahl., 1812, an Willd. ? 



D. Wahlenbergii, Hartm. 1820. D. Lapponica, DC. Syst., an Willd.? D. nivalis, DC, non Lilj. 



2. B, Fladnitzensis, Wulf., Jacq. Misc. 



D. lactea, Adams. ? D. Carinthiaca, Hoppe. D. crassifolia, Grab. 



3. B. muricella, Wahl. 



D, nivalis, UX]., nan J}G. 



4. B. rupestris, Br. 



D, Altaica, Bge. 



5. B. hirta, L. 



D. Dovrensis, Fr. D. arctica, Vahl. 



6. B. incana, L. 



D. contorta, Ehr. D. confusa, Ehr. & DC. D. Thomasii, Koch. 

 VOL. XXIII. 2 u 



