SKETCH OF THE FLORA OF ALASKA. 439 



proportion of 1 to 4.5. In marked contrast to tlie foregoing is the following from 

 the same author : 



'' The Arctic circle at Kotzebue sound is crossed by the isotherm of 23°, and 

 at the longitude of the Mackenzie by that of 12° 5', while the June isotlierm of 

 41° ascends obliquely from southwest to northeast, from the Aleutian islands to 

 the mouth of the Mackenzie, and passes south of this province ; the June and 

 September isotherms of 41° and 32° both traverse it obliquely, ascending to the 

 northeast. The vast extent of the Pacific ocean and its warm northerly cim'- 

 rents greatly modify the climate of west Arctic America, causing dense fogs to 

 prevail, especially throughout the summer months, while the cuixents keep the 

 ice to the north of Behring's strait." 



In this Arctic Alaskan district we have 76 monoctyledons and 288 dicotyle- 

 dons, giving a proportion of 1 to 3.7. Dr. Hooker finds in "comparing this 

 flora with that of temperate and Arctic Asia that no less than 320 species are 

 found on the northwestern shores and islands of that continent, or in Siberia, 

 many extending to the Altai and the Himalaya. A comparison with eastern 

 Arctic America shows that 281 species are common to it." Of the 364 species 

 of Arctic Alaskan plants "almost all but the littoral and purely Arctic species 

 are found in west temperate North America or in the Rocky moimtains, 26 in the 

 Andes of tropical or sub-tropical America, and 37 in temperate or Antarctic 

 Sotith America." 



Tlie above paragraph affords an excellent ilhistration of the migration south- 

 ward of northern plants during a period of cold long since past. Whether we 

 clothe this joint explanation of Messrs. Forbes and Darwin with all the dignity 

 of a theory logically deduced from other and well-established facts, or reduce it to 

 the rank of a mere hupotlicsis, it still remains the onhj pluhsophical explanation 

 of these examples of widely-extended distribution along a given meridian. 



Dr. Hooker also directs attention to the variety, of glumacese in the Ai'ctic 

 Alaskan flora: "Of the 138 species of Arctic glumaceae only 54 are natives of 

 west Arctic America." 



I insert here the following letter from Mr. H. M. Bannister, who spent the 

 winter of 1865-66 at Fort St. Michaels, on Norton Sound. It is to the point 

 and explains itself: 



"I am sorry that I can give from personal observation so little information 

 concerning the trees of Russian America. At St. Michaels there were no trees, 

 and the only bushes which rose above the ground were stunted alders and wil- 

 lows. At the head of Norton sound, however, a forest of spruce trees extends 

 nearly to the coast, and occasional trees are seen on the immediate shore. These 

 trees are usually from 20 to 45 feet high and not more than a foot in diameter. 



" The drift logs which float on the Kvichpak are sometimes more than two feet 

 in thickness, though the most will not average over a foot or 16 inches. I think 

 it probable the largest trees do not grow where they will be undermined by the 

 river cuiTcnt. 



" ]\Ir. Pease reported having seen trees nearly 80 or ] 00 feet high on the lower 

 Kvichpak. From 1,000 to 1,500 feet of lumber was saAvn at Fort St. Michaels 

 during the winter I was there. It made very fair-looking planks and scantling. 

 I thhik the wood was softer and whiter than that of the Oregon pine. The 

 other trees noticed were poplars and birch ; of how many kinds I cannot say. 

 The birch is used by the natives for everything that requires a harder and tougher 

 wood than the spruce, /. e., sled-runners, boat-frames, &;c. I have never seen 

 birch there over eight inches in diameter." 



In looking over the plants collected by ]\Iessrs. Dall, McDonald, and Houlc, 

 at Fort Youkon, I have been surprised to see how large a number of them were 

 common on the head-waters of the Mackenzie and the Pelly. Whether Fort 

 Youkon can be considered a point which in their wanderings from more southern 

 localities they might reach, I am not prepared to say ; possibly the waters of 



