The Origin of Sphagnum Atolls. 
25 * 
height and regularity of the banks of the parent pond ; (c) a regular 
and gentle slope of the pond bottom from shore to centre; (d) a 
definite original character of littoral vegetation when the pond 
was at low level; ( e) a reduction within minimum limits of the 
lateral pressure and tension of winter ice; (f) a comparatively 
prompt anchoring of the atoll upon the bottom.” 
Atkinson (2) states that the shade of overhanging trees of the 
banks is probably responsible for the marginal trench. Shaw (3) de¬ 
scribes some curious ponds near Woods Hole which are not to 
be understood as sphagnum atolls and in all probability their 
development is due to the factors that he mentions. 
From the description of MacMillan, the Ballard atoll in 1894 
was surrounded by a narrow zone of Care.x with such subdominants as 
jfuncus, Iris, Utricularia, and Potentilla. The atoll was covered 
with Chamcedaphne, Andromeda, Oxycoccus, Kahnia and character¬ 
istic herbs of this associes, such as Sarracenia, Eriopiiorum, and 
Menyanthes. This bog is at present a Carcx-Calamagrostis meadow 
in which a few small spruce and tamarack trees remain on 
sphagnum hummocks near the north end. The outer zone of the 
Anderson atoll, as MacMillan reported it, consisted of “ a luxuriant 
growth of Panicularia fluitans (Linn.) OK. mingled with the following 
in less abundance: Typha,Potamogeton, Sagittaria, Phragmites, Poly¬ 
gonum, and Utricularia. The vegetation of the atoll itself, except 
for the presence of the same three species of Sphagnum and a very 
abundant growth of Limodorum, differed entirely from that of 
Ballard’s atoll. The most conspicuous plant was Picea mariana 
(Mill.) B.S.P. Twenty-seven young trees of this species—the 
black spruce—had established themselves upon the atoll. The 
largest was but four and one-half feet in height, while the smallest 
noted was not over eight inches. These trees, evenly distributed, 
occupied the middle of the ribbon of sphagnum and presented a 
most attractive and unusual appearance, forming as they did an 
almost perfect ring about the open, placid and central lagoon. 
Next in importance, as giving character to the atoll, was a dense 
growth of Ledum latifolium Ait.—Labrador tea—which covered 
almost the entire island. “ The lagoon of this atoll, unlike that 
of the other, was somewhat invaded with floating vegetation— 
mostly Utricularia intermedia Hayne, with a few plants of 
Panicularia.” 
The Anderson bog is to-day a wet meadow with a few sphag¬ 
num hummocks here and there, which vary in size from a few 
