Vegetation Assemblage 19¢ 
Concerning soil condiéions in general during the growing season reference 
may be made to Leffingwell! who observed: 
_ “Above the permanently frozen ground there is everywhere a layer 
which is alternately frozen and thawed each year. The thickness of 
this layer, though primarily dependent upon the warmth of the sun, is. 
yet so greatly influenced by the nature of the soil that it is quite variable. 
Porous gravels and sand will thaw many times as deep as muck or clay.” 
The limit of seasonal thawing is therefore anywhere from a few inches to 
several feet. The thawing is least pronounced where the ground is covered by 
ee permanent snow or ice, or where it is sheltered by driftwood, bould- 
ers, etc. 
To this may be added from Leffingwell?:— 
: “At present the coastal plain is free from snow scarcely three months 
in the year... . The temperature of the plain adjacent to the Arctic Ocean 
is kept in the neighbourhood of freezing by the presence of ice-laden 
waters. Inland the temperature is much higher. ... Consequently not 
only would the accumulation of snow be greater near the coast, but the 
subsequent melting less.” 
Concerning the climate of Herschel island reference may be made to Preble? 
who gives a summary of the monthly temperatures for the year 1900. According 
to the monthly mean temperature, the months of 1900 arrange themselves, - 
beginning with the colder ones, as follows: January, February, December, 
March, November, April, October, May, September, June, August, July. The 
two extreme monthly mean temperatures for the year in question are —22-6°F. 
and 42-7°F. with a minimum of —49-4°F. and a maximum of 62-8°F. 
VEGETATION 
Many of the explorers and travellers visiting the coast between point 
Barrow and Mackenzie delta have collected samples of the vegetation in different 
localities, and lists of the plants collected have been published in the accounts 
of the various expeditions and elsewhere. Nowhere, however, does one find a 
general description of the vegetation on any part of the coast, and when herewith 
an attempt is being made to supply such a description, it should be 
remembered that my personal acquaintance with the coast in summer time is 
limited to a few localities, and to no locality for a whole season. 
In describing the vegetation along the coast between point Barrow and 
Mackenzie delta the subject will be dealt with under two main headings, viz.: 
the beach vegetation and the vegetation of the Coastal plain proper. To these 
will be added a third chapter giving a general account of the vegetation of 
Herschel island which, as intimated in preceding pages, may topographically 
be considered an out-runner of the Plateau. 
THE BrAcH VEGETATION 
The beach region includes sand flats, especially at river mouths, and sand 
spits, gravel bars, etc., on the mainland, together with many islands, mostly 
small, built up of similar material and stretching along the coast. My observa- 
tions about the vegetation of the beach region are limited to Spy island, east of 
Thetis island, Konganevik, Collinson point, and the mouth of the Hulahula river 
at Camden bay, Martin point, Icy reef and Demarcation point farther east, all 
west of the international boundary line. Though the typical and dominant 
plants are the same on the gravel islands and on the mainland, it must be borne 
in mind that the conditions for the spreading of the more typical tundra plants 
1 The Canning River Region, etc., r es 
oe BA North Aoneriean Fauna No. 27, 1908, p. 35. 
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