Io BOTANICAL GAZETTE [JANUARY 
Evidencing the retardation of the season is the fact that ice 
frequently remains in sheltered places on the northwest coast of 
the island into July. I have seen a deserted mine shaft filled solid 
with ice on July 4. Foster and WHITNEY report ice ‘under the 
shade of crags, and among the thick evergreen swamps of white 
« cedar.” 
In precipitation there is apparently not -much difference between 
Port Arthur and Isle Royale, at least during the growing season. 
As far as the records go the mainland has a slight advantage. 
TABLE V 
AVERAGE PRECIPITATION May-—Nov., 1906-1909 
eee Eb ee ee es oa eS 48.00 cm. 
Peeeree SAIN os ss ee Se ee 43.74 cm. 
From the foregoing data, which unfortunately are rather frag- 
mentary, it appears that there is at present no ground for concluding 
that the island climate is effective in producing a more mesophytic 
type of vegetation than that of the mainland, or vice versa. The 
lower evaporation rate upon the island, due to lower temperature, 
is balanced by a less precipitation during the growing season; and 
the growing season, although retarded in its commencement upon 
the island, is apparently as long as upon the mainland. The 
question cannot fully be settled without fuller precipitation records 
from Isle Royale and a determination of the actual evaporation 
rates in the two localities. The data presented, however, indicate, 
so far as they go, that the insular position of the field of study does 
not seriously affect its value as a fair sample of the region dominated 
by the northeastern conifer forest. 
Part I.—The climax forest 
The forest that completely clothes the surface of Isle Royale, 
with the exception of a part of the bog areas, some limited stretches 
of xerophytic character, and the small portion dominated by the 
maple, is made up largely of three trees: Abies balsamea (L.) Mill 
(balsam fir), Betula alba L. var. papyrifera (Marsh) Spach (paper 
birch), and Picea canadensis (Mill) BSP (white spruce). The 
studies embodied in the present paper show that this type is the 
