RECENT INVESTIGATIONS. 27 



soil is kept moist, and a moderate degree of heat as well. Drouth during 

 spring or early summer is unfavorable to grassland. A woodland climate 

 leads to victory for woodland, a grassland climate to victory for grassland. In 

 transition climates, edaphic influences decide the outcome. Strong deviations 

 from woodland or grassland climate produce desert. Definite properties of 

 the soil may bring forth a character of vegetation that belongs to none of the 

 climatic types. These demand a soil congenial to the vast majority of plants. 

 Extreme soil conditions unfavorable to most plants set vegetation free from 

 the controlhng influence of rainfall. Consequently, the vegetation of rocks, 

 gravel, swamps, etc., bears in the highest degree the impress of the substratum, 

 and this impress usually remains identical under very different climatic 

 humidities, which on such soils play only a subordinate part. 



In spite of the successional significance of climatic and edaphic communities, 

 Schimper {I. c, 185) seems to have had only a general idea of the development 

 of vegetation, for he not only states that little attention had been paid to it, 

 but also cites only Treub's study of Krakatoa and the work of Flahault and 

 Combres on the Camargue as examples of it. While his open edaphic forma- 

 tions are in the main stages in successional development, as he recognizes in 

 certain cases, fringing forests are portions of climax and hence climatic forma- 

 tions, as is well shown by every large stream of the prairie region. The fact 

 that he does not regard edaphic formations as mostly or primarily develop- 

 mental is shown by the subdivision into edaphic formations due to telluric 

 water (swamps, moors) and open edaphic formations (rocks, dunes). The 

 latter alone are regarded as showing a transition from edaphic into climatic 

 formations. How close he came to the basic distinction between develop- 

 mental and climax conomunities, and how his concept of edaphic and climatic 

 formations caused him to miss the real relation may be gathered from the 

 following excerpt : 



"Transition from Edaphic to Climatic Formations: Between the bare hard 

 rock and the finely grained soil that finally results from it, for the possession 

 of which there is a struggle between woodland and grassland, according to 

 what has been said above, there is a series of open transitional formations, 

 which possess the character neither of woodland nor of grassland, and which 

 assume nearly the same appearance even in dissimilar climates, and owe their 

 individuality chiefly to the mechanical texture of the soil. The transforma- 

 tion of these transitional formations into the definite ones of woodland and 

 grassland is continually proceeding under our eyes, but so slowly that we can 

 observe only a part of the process directly, and can form an estimate of their 

 sequence only by comparing their condition at different ages. In spite of the 

 highly interesting nature of the devdopment of formations, very slight atten- 

 tion has hitherto been paid to it." 



Schimper's climatic formations are for the most part the climax formations 

 of the present treatise, and his edaphic and transition formations are develop- 

 mental units, associes, and consocies. This is essentially the conclusion 

 reached by Skottsberg, though in different terms (1910:5). 



Cowles, 1899. — ^The first comprehensive study of succession in America was 

 that of Cowles (1899 : 95) upon the sand-dunes of Lake Michigan. Together 

 with the dune studies of Warming already mentioned, it has served as a model 

 for the investigation of dune succession the world over. The methods of 

 physiography were employed, inasmuch as the flora of a particular area was 



