186 ECOLOGY 



green crown," and "leafless, perennial succulents," in place of the 

 systematic names of orders whose predominance characterizes a given 

 landscape, such as conifers, palms, and cacti. The leaves have come 

 to be more and more regarded as a distinguishing characteristic, 

 and to them is dedicated Hansgirg's Phyllobiologie, in which they 

 are classified according to their pubescence, their flexible or rigid 

 character, or according to their structure for protection from light, 

 wind, or rain, or the method they adopt for shedding water, either 

 by means of "spouts," or of an impervious wax covering. It 

 is their structure which bears the imprint of the climatic seal and 

 determines the fundamental form of tree, shrub, bulb, and mat, 

 just as their period of activity determines the length of the season. 

 Thus in groups formed according to leaf and vegetative period, we 

 naturally find the most diversified sub-groups, among which may be 

 reckoned those classified according to the mode of displaying the 

 flower, the manner in which it is fertilized, the protection of the pollen 

 from rain, or the characteristics of parasitic or insectivorous plants, 

 while there may still be others arranged according to the station, 

 either in light or shade, on dry or moist soil, or humus or on rock. 

 As yet, science has not succeeded in obtaining a satisfactory 

 enumeration of the separate ecological forms, for this, the science in 

 its anatomical and physiological aspect is still too young, but it is 

 a pleasure to see the increase in investigation along these lines and 

 the severe criticism to which the results are subjected. For the 

 future, we can predict a classification of living forms, which, based 

 upon observation of external appearance, will appeal to a far larger 

 circle than do the intricacies of phylogenetic research, whose 

 embodiment in a system offers just as great difficulties to the more 

 formal methods of classification. 



(2) Ecology is the doctrine of reciprocal biological relations and 

 of the adaptations acquired in the struggle for space and necessi- 

 tated by the existing conditions of soil and climate; we may there- 

 fore consider that these terms show us the links by which ecology 

 is indissolubly bound to the geographical sciences. Still, it would 

 not be right to consider botanical geography as only the same 

 matter as botanical ecology, since, taken by itself, and without due 

 regard to the ecological interpretation of phenomena, there exists 

 also an abstract, geographical method of considering the organic 

 world. 



If, however, we survey the organic world from the geographical 

 point of view, it seems to us of the utmost importance to divide it 

 into organic districts which will represent the essential characteristics 

 of continents, islands, mid-ocean, and seacoast. From the biological 

 point of view it seems of the utmost importance to discover the 



