4 TILE FOUNDATION OF ECOLOGY 
the small number of successions so far studied. Future progress in this 
field will be conditioned not only by the more frequent study of develop- 
mental problems by working ecologists, but also, and most especially, by 
the application of known principles of succession, and by the working out 
of new ones. 
6. Ecological phytogeography. Until recent years, the almost universal 
tendency was to give attention to formations from the standpoint of vegeta- 
tion alone. While the habitat was touched here and there by isolated work- 
ers, and plant functions were being studied intensively by physiologists, 
both were practically ignored by ecologists as a class. The appearance of 
Warming’s Lehrbuch der oecologischen PAanzengeographie (1896) and of 
Schimper’s Phanzengeographie auf physiologischer Grundlage (1898) rem- 
edied this condition in a measure by a general discussion of the habitat, and by 
emphasizing the importance of the ecological or physiological point of view. 
Despite their frank recognition of the unique value of the habitat, the major 
part of both books was necessarily given to what may be termed the general 
description of formations. For this reason, and for others arising out of 
an almost complete dearth of methods of investigation, ecology is still al- 
most entirely a floristic study in practice, although there is a universal recog- 
nition of the much greater value of the viewpoint which rests upon the 
relation between the formation and its habitat. 
7. Experimental ecology. Properly speaking, the experimental study of 
ecology dates from Bonnier? (1890, 1895), though. it is well understood that 
experimental adjustment of plants to certain physical factors had been the 
subject of investigation before this time. The chief merit of Bonnier’s 
work, however, lies in the fact that it was done out of doors, under natural 
conditions, and for these reasons it should be regarded as the real begin- 
ning of this subject. Bonnier’s experiments were made for the purpose of 
determining the effect of altitude. Culture plots of certain species were 
located in the Alps and the Pyrenees, and the results were compared with 
control cultures made in the lowlands about Paris. In 1894 he also made 
'BonnNIER, G. 
Les Plantes Arctiques Comparées aux Mémes Espéces des Alps et des Pyrénées. 
Rev. Gen. Bot. 6:505. 1894. 
Cultures Expérimentales dans les Alps et les Pyrénées. Rev. Gen. Bot. 2:514, 1890. 
Recherches Expérimentales sur |’Adaptation des Plantes au Climat Alpin. Ann. 
Nat. Sci. 7:20:218. 1895. 
BonnikEr, G., ET CH. FLAHAULT 
Modifications des végétaux sur l’influence des conditions physiques du milieu. 
Ann. Nat. Sci. 6:7:93. 1878, 
