438 SKETCH OF THE FLORA OF ALASKA. 



mainland north of Norton sound I am indebted to Dr. Seemann, op. citat. — J. T. R. | 



Cbamisso writes of Kotzebue sound that "the vegetation is much more luxu- 

 riant than in St. LawTence cove," (some distance further to the north on the 

 Siberian side;) "the willows are taller, the grass grows stronger, all the plants 

 are more stout and succulent, while the greater number of species common to 

 the American coast than appear in St. Lawrence cove, indicate a more temperate 

 climate. On the island of St. Lawrence the Cineraria palustris grows with a 

 remarkable luxuriance in the well-watered slopes formed at the base of the mounds 

 of ice, while Bctida nana (dwarf birch) is seen even to the very shores. The 

 plain countiy of this island is free from snow throughout the summer." 



It will be observed that Mr. Seemann draws a line from the mouth of the river 

 Noatak in a northeasterly direction across the country almost to the estuary of 

 Mackenzie river ; this he assigns as the northern limit of the woods. This line 

 nearl}- coincides with the July isotherm of 50°, which temperature may be 

 regarded as a fair growing mean for the species of that region. 



Beyond this all plant life is truly Arctic, and comes within the scope of Dr. 

 Hooker's paper on the Distribution of Arctic Plants. The distinguished author 

 just named divides the Arctic circle around the globe into five districts. Going 

 east from Baffin's bay wo have, first, the Greenland district 5 the second one lies 

 between the western coast of Arctic Europe, and extends as far to the east as 

 the river Obi, and includes Nova Zembla and Spitzbergen ; the third extends 

 from the Obi river to Behring's strait ; the fourth from Bchring's strait to the 

 Mackenzie river ; and the fifth from j\Lackenzie river to Baffin's bay. Primarily 

 we are concerned with but three of these divisions : first, the fourth or Arctic 

 Alaskan, and then merely en xiassant \vith the third and fifth lying on either side 

 of it. From the same paper we learn that the fourth district has of flowering 

 plants 364 species, (the teiTn species being 'used by Hooker in a very wide sense, 

 and all forms which are not clearly marked are regarded merely as boreal varie- 

 ties of some older species.) Of these 364 (flowering) species, 110 of them are 

 Asiatic and American forms ; the third or Arctic Siberian district contains 233 

 species, and of them but 44 are peculiarly Asiatic and American ; the fifth or 

 Arctic eastern American has 379, and of them 110 are peculiarly Asiatic and 

 American. From the above it will bo seen that the Arctic Alaskan district has 

 a flora much richer both in specific aud pecuZ/ar specific forms than the Siberian 

 district, but is not cpiite so rich in species as the fifth or eastern American ; the 

 northern limits of vegetation will var}^ in different longitudes. Rather a rich 

 vegetation clothes the Arctic Alaskan shores, judging from the number of plants 

 collected by Captain Pullen. Herald island, however, in latitude 72° north and 

 longitude 176° west, rewarded Seemann's search with but four species. Eastern 

 Greenland, between 70° and 75° north, gives 150 species. The reason of this 

 disparity in numbers is, in part, found in the following passages : 



" The climate of eastern Arctic Asia is marked by excessive mean cold ; at 

 the Obi the isotherm of 18° cuts the Arctic circle in its southeast course, and at 

 the eastern extremitj^ of the province the isotherm of 20° cuts the same circle, 

 while the centre part of the district is all north of the isotherm of 9°. The 

 whole of the district is hence far north of the isotherm of 32°, which descends 

 to latitude 52° north in its middle longitude. The extremes of temperature are 

 also very great; the Juno isotherm of 41° ascending eastward through its west- 

 ern half to the Polar sea, while the September isotherm of 41° descends nearly 

 to 60° north ; whence the low autumn temperature must present an almost insu- 

 perable obstacle to the ripening of seeds within this segment of the Arctic circle. 

 "The warming influence of the Atlantic currents being felt no further east 

 than the Obi, and the summer desiccation of the vast Asiatic continent, combine 

 to render the climate of this region one of excessive drought as well as of cold; 

 whence it is in every way most unfavorable to vegetation of all kinds." 



Of its 233 species 42 are monoctyledous and 191 are dicotyledons, making a 



