386 Forestry Quarterly 



towards the sum total of ecological knowldege were De Can- 

 dolle, Schouw, Engler, von Humboldt, Drude, Schimper, and 

 Warming. 



The last half of the 19th century was given over to investiga- 

 tions and writings (2, 3, 4, 5, 6) upon the nature of plant forma- 

 tions, their development, behavior, and classification. It was in 

 this period that certain phases of vegetation known as association, 

 succession, and invasion were studied and vague ideas about these 

 phenomena began to crystallize into definite conceptions. But it 

 was not until 1895 that a definite advance was made in this direc- 

 tion. In that year, Warming (7) made the first attempt to 

 treat the then new subject of "©ecological plant geography" and 

 to compile the data that had accumulated up to that time into a 

 book, guided by a few general principles. 



Since 1895, the tendency has been to study plant formations 

 more critically. The emphasis has been shifted from the forma- 

 tion to the h-abitat. The works of Drude (8), Warming (9), and 

 Schimper (10) bear witness to this new development of the 

 science. The encyclopaedic work of Schimper not only treats of 

 habitat factors as preliminary to a discussion of plant formations 

 and associations, but it also emphasizes the physiological point of 

 view in plant ecology. Both of these facts are unmistakaible ear- 

 marks of the modern trend of ecological thought. 



Experimental plant ecology, another phase of the science which 

 has developed only very recently, may be said to have taken its 

 beginning in the experiments of Bonnier between 1890 and 1895 

 (11, 12, 13). His experiments in determining the effect of alti- 

 tude upon plant development, being performed under natural 

 conditions, may be said to be the real beginning of field investiga- 

 tions in plant ecology. W^e are indebted to him also for the first 

 attempt, in this connection, of ascribing changes in plant struc- 

 ture to a definite cause. 



The determination of the physical factors of the habitat begins 

 about this time. In the early nineties, Ramann, a great student 

 of soil physics and soil chemistry, made what were among the 

 first soil moisture measurements in the vicinity of Eberswalde, 

 Germany, to determine the moisture content of difl^erent kinds of 

 soils and also the variations in soil moisture content arising from 

 different methods of forest regeneration. It is interesting to note 

 that Ramann was chiefly an investigator of soils from the forestry 



