NOTES AND ABSTRACTS. 



285 



occidcntalis are specially important. After these forerunners have 

 had their day, the trees of the climax forest begin to appear. 



3. Rock pools are usually occupied by Scirpus caespitosus ; Poly- 

 trichum forming a turf mat on which V actinium, Andromeda, and Alnus 

 establish themselves. 



These three different successions are finally united in a (4) Heath 

 mat chiefly by the agency of Juniperus, Arctostaphylos, and Thuja 

 occidentalis. This may be forthwith annexed by the climax forest 

 or there may be an intermediate type of dry-climate forest (5) in 

 which Pinus Banksiana, Picea mariana (black spruce), and occasionally 

 aspen are dominant forms. 



On the Gull Islands was found a somewhat different succession, in 

 which Calamagrostis canadensis and Pyrus americana were prominent 

 species. A similar vegetation may have been the first to occupy 

 the summit of the ridges of Isle Royale when they first emerged from 

 the glacial waters of Lake Duluth. 



Along beaches of sand or shingle the climax forest soon covers 

 the ground, but is usually fringed by a line of Alnus crispa, and along 

 the shingles by pioneer species such as Equisetum arvense, Epilobium 

 angustifolium, Deschampsia caespitosa, Rubus, Rosa, and Salix. The 

 lakes are occupied at first by aquatics, Isoetes, Chara, Potamogeton. 

 There is also a water-lily zone and one of amphibious plants, such as 

 Menyanthes and Lysimachia thyrsifiora, which are often mat-formers. 

 These are followed by the bog forest, in which Larix americana, Picea 

 mariana, and Alnus incana are the most important. In other places 

 Carex filiformis, Eleocharis palustris, and Equisetum fluviatile form a 

 sedge mat, the first named being the most important. 



Sphagnum forms, in the lakes described, a superficial layer upon 

 the sedge mat and does not contribute in any large degree to peat 

 formation. It begins some distance within the margin of the bog 

 and works outwards and towards the centre. It grows up round 

 those shrubs, such as Chamaedaphne and Andromeda, which are estab- 

 lished on the sedge mat, and on its surface are found Sundew, Oxycoccos, 

 Carex pauci flora, and Smilacina. The Sphagnum is then colonized 

 and suppressed by Ledum groenlandicum, and this last is invaded by 

 the bog-forest of tamarack and black spruce, which are again super- 

 seded by the climax forest. The delta swamp succession is also 

 described, the stages being Potamogeton, Equisetum, sedge mat and 

 bog herbs, Myrica Gale, Alnus and other shrubs, swamp forest with 

 Fraxinus nigra as pioneer, then the trees of the climax forest. 



When the forest has been burnt down, but without destroying 

 the humus, the first growing season shows a profusion of Epilobium 

 angustifolium and Anaphalis margaritacea ; seedling birches and 

 poplars, with Rubus Idaeus, Diervilla, Corylus, &c, follows, and 

 bracken, Aster, and others replace the Epilobium. 



The bibliography seems almost entirely American, but even this 

 short abstract will remind European readers of closely parallel succes- 

 sions in the Old World, and those who consult the original will find 



