RECENT INVESTIGATIONS. 25 



eventually occupy the whole area, as is evidenced by the circular or elliptical 

 tamarack communities frequent in southern Minnesota. After the tamarack 

 area has become sohd, the Sphagnum often persists in little clumps and mats 

 at the bases of the trees. Sarracenia, Vaccinium, etc., also linger for some 

 time, but Eriophorum, Salix, and many other species disappear because of 

 the shade. 



As to the origin of a solid or spruce-centered consocies of tamarack, it is 

 doubtful whether a stage with central moor ever existed. In some cases, suc- 

 cessions of muskeag openings with intervening tamarack arise from the filling 

 of a lake with bars or reefs upon its bottom. Some of the circular tamarack 

 swamps with or without spruce cores were not necessarily derived from moors 

 with tamarack or tamarack-spruce border-rings, though most of the sohd 

 tamarack swamps must have developed by the closing in of a ring of timber 

 upon a constantly diminishing moor. Finally, the author remarks signifi- 

 cantly that "the contemplation of vegetation in any region with these prin- 

 ciples in view is certainly interesting. Practically it connects at once ecologic 

 distribution with physiography, and enlarges the content both of topography 

 and botany." 



Warming, iS95.— Warming made the first attempt (c/. 1896:350; 1909: 

 348) to deal with succession in a general fashion, though his treatment was 

 brief and largely incidental to the main purpose of his work. This is empha- 

 sized by the fact that the text devoted to this subject is practically unchanged 

 in the second edition of his book, in spite of a lapse of 14 years marked by a 

 great advance in developmental ecology. Nevertheless, Wanning deserves 

 great credit for being the first to try to organize this vast field. In the last 

 edition the section which deals with development is headed "Struggle between 

 plant-communities," and is subdivided into 7 chapters, namely: (1) Condi- 

 tions of the Struggle; (2) The Peopling of New Soil; (3) Changes in Vegetation 

 Induced by Slow Changes in Soil Fully Occupied lay Plants, or Succession of 

 Vegetation; (4) Change of Vegetation without Change of Climate or Soil; 

 (5) The Weapons of Species; (6) Rare Species; (7) Origin of Species. The 

 last two obviously have only a remote connection with succession as a process. 

 The discussion of the pedphng of new soil deals with the origin of bare soil 

 areas and the vegetation which arises upon them. The following chapter 

 upon the succession of vegetation treats primarily of water and rock seres, and 

 especially of the conversion of moor and forest. The chapter on the peopling 

 of new soil is divided into (1) vegetation on sand, (2) production of marsh, 

 (3) lowering of water-level, (4) volcanic eruptions, (5) landslips, (6) fires in 

 forest and grassland, (7) other sources of new soil, (8) sunomary of results. 

 In the latter, six fundamental principles are laid down; these deal with the 

 pioneers, number of species, life-forms, migration-forms, light relations, and 

 the distinction into initial, transitional, and final communities. The copious 

 citation of papers on development makes the treatment a very helpful intro- 

 duction to the subject. 



Graebner, 1895. — Graebner (1895: 58) was the first to make a comprehensive 

 study of the development of a great climax or subclimax commxmity. The 

 developmental relations of the heath of northern Germany are considered in 

 three sections: (1) Origin of the Heath Formation; (2) Changes of Heath Vege- 

 tation; (3) Culture of Heath; while the physical factors are discussed under 



