Oekologle. 5J 



Lines, mesurant 30 ä 35 ,«, sont lisses et portent les trois lignes 

 divergentes caracteristiques des macrospores; les autres, de meme 

 taille et contenues dans les memes sporanges, montrent ä leur 

 Interieur un tissu forme de quelques cellules, qui doivent avoir 

 contenu les cellules meres des anth^rozoides. 



Sur d'autres pinnules, M. Renault a rencontre des 

 sporanges pedicelles, munis d'un anneau longitudinal assez 

 analogue ä celui des Larkeriees, et renfermant des spores 

 triangulaires ä exospore epaisse, marqu^e de trois lignes radiantes 

 caracteristiques des macrospores. 



L'auteur conclut que les Fougeres, Eusporangiees et Lepto- 

 sporangiees, ont eu ä l'epoque houillere des representants 

 heterospores. r. Zeiller. 



CoWLES, Henry, C, The Physiographic Ecology of 

 Chicago and Vicinity; a Study of the Origin, 

 Development, and Classification of PlantSocieties. 

 (Contributions from the Hüll Botanical Laboratory. XXIV. 

 Botan. Gaz. XXXI. 73—108; 145—182. 1901. With 35 text. 

 figures.) 



Difficulties having been found in satisfactorily classifying 

 plant societies into hydrophytes, mesophytes, and Xerophytes, 

 an attempt is made to develop a genetic and dynamic Classi- 

 fication. This Classification is essentially physiographic, since 

 it is based on the well known laws of topographic change. 

 The tendency of a land mass to approach a base level by the 

 denudation of uplands and by deposition on the lowlands may 

 be expressed in ecological terms as the tendency to approach 

 a uniform ecological condition. In the favorable climate of the 

 northeastern United States the xerophytic uplands and hy- 

 drophytic swamps and lakes incident to a young topography tend 

 to becom.e more and more mesophytic. There is then a definite 

 Order of succession of plant societies which characterizes the 

 life history of each topographic type, though this order may 

 not be the same in different regions. Locally there may be 

 retrogressive stages of development away from the mesophytic 

 condition. Crustal movements and climatic changes modify 

 but do not essentially alter the laws of physiographic change. 



An application of these principles is made for the region 

 about Chicago. Five series are traced from the primeval con- 

 dition to the mesophytic forest, which is the culminating type 

 in that region. 1) Ravines, whether of rock or clay, are at 

 first xerophytic; on account of favorable conditions they may 

 soon attain a temporary mesophytic condition. Widening and 

 deepening cause semi-xerophytic conditions to recur, but ulti- 

 mately the gentle slopes of an old topography are covered by 

 mesophytic forms. The flood plains, hydrophytic at the outset. 

 ultimately develop a high grade of mesophytic forest. 2) Un- 

 drained depressions may at first contain ponds. By the rapid 



