MacMillan: OCCURRENCE OF SPHAGNUM ATOLLS. 5 



cality on Ballard's atoll is the first, and as yet the only one for 

 this plant, in central Minnesota. It has previously been re- 

 ported from the north shore of lake Superior by Messrs. 

 Sandberg, Alton and Schmidt. The two orchids — Pogonia and 

 Limodorum — are rare plants in central Minnesota and Eriopho- 

 rum vaginatum Linn, is comparatively infrequent. On the 

 atoll there was a distinct arrangement of species which is of 

 interest. Menyanthes trifoliata Linn, was most abundant on 

 the outer and inner edges. Kalmia occupied five distinct 

 patches, being abundant in these areas, but not between. The 

 Sarracenia and Eriophorum occupied the central position in the 

 atoll-ribbon and .sought apparently the firmer substratmu. 

 Oxycoccus and Andromeda were sparingly represented. Only 

 a dozen or so plants of Lyonia were observed. 



General description of Anderson's atoll. This atoll oc- 

 curs in a small pond tributary to the north bay of lower Gull 

 lake. The pond is barely fifty yards across, with high banks, 

 and the atoll ring is within a foot or two of twenty yards in di- 

 ameter. Its breadth, however, is greater than that of Bal- 

 lard's atoll, being twelve feet on the average from the outer to 

 the inner aspect. The lagoon, then, is slightly less than fifty 

 feet across. The pond-waters outside are clothed with a luxu- 

 riant growth of Panicularia fluitans (Linn.) OK. mingled with 

 the following in less abundance: 



Typha latifolia Linn. — Cat-tail. 



Potamogeton zosteraefolius Schum. — Pondweed. 



Sagittaria sagittaefolia Linn. — Arrow-head. 



Phragmites phragmites (Linn.)Karst. — Reed grass. » 



Polygonum emersum (Mx.) Britt. — Smartweed. 



Utricularia intermedia Hayne. — Bladderwort. 



The water of the pond was shallow, averaging four feet, just 

 outside of the atoll- ring. 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, w^hile 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 opan. placid and central lagoon. Next in im- 



