66 OECOLOGICAL FACTORS AND THEIR ACTION sect, i 



Many species of plants are very indifferent as regards soil, inasmuch 

 as they can grow on widely dissimilar kinds, for example : Phragmites 

 communis grows both in very saline and in fresh water ; and Typha 

 latifolia is said by Sickenberger to be capable of growing vigorously in 

 the soda-lakes of Egypt, where a nearly saturated solution of salts is 

 present. Many ubiquitous or cosmopolitan species display but little 

 preference, yet most species are confined to soil that has quite definite 

 physical and chemical relationships. 



Long ago it was noticed, particularly in mountainous countries with 

 a substratum of varied geognostic nature, that the distribution of species 

 and the whole appearance of the vegetation show a certain correlation with 

 the soil. As an example we may select the case treated by Petry ^ of 

 the Kyffhauser Hill, where there is a sharp contrast between the vegeta- 

 tion on the rothliegende and that on the zechstein, not only in the forest 

 and in its undergrowth, but also in the weed-flora, the vegetation of the 

 sunny dry heights, and of the copses. The rothliegende, as a conse- 

 quence of its poverty in nutriment, supports a meagre, uniform vegetation, 

 partially agreeing with heath ; the zechstein tract, on the other hand, 

 has beech-forests and a herbaceous flora of many species. The contrast 

 between the two sub-formations is so sharp that we can detect from the 

 vegetation, either in forest or field, whether we are standing upon the 

 one or upon the other ; and the relations are such that this contrast 

 must be attributed to conditions prevailing in the soil. 



Similarly in Montpellier,^ in Switzerland,^ and in many other moun- 

 tainous lands we can observe the most emphatic contrast in the vegetation 

 of two contiguous tracts, and even in a moraine-country like Denmark 

 the same can be observed. In Jutland we can see sharply delimited 

 patches with the Weingaertneria-association (Corynephorus-association), 

 containing Weingaertneria canescens, Trifolium arvense, Scleranthus, 

 Hieracium Pilosella, and others, dotted about a tract which hkewise 

 has a poor arable soil, but which supports an entirely different vegetation 

 composed of Leontodon autumnale, Jasione, Lotus corniculatus, Erigeron 

 acris, Euphrasia officinalis, Trifolium pratense, T. repens, Achillea Mille- 

 folium, Chrysanthemum Leucanthemum, Equisetum arvense, and others : 

 in the former areas there are no mole-hills, whereas in the latter there are 

 many. 



The reasons for these generally observed distinctions have been 

 sought chiefly in two directions. Some authorities regarded the chemical 

 constitution of soil as the decisive factor, while others laid greatest stress 

 upon the physical characters, and particularly upon the relations prevailing 

 in regard to heat and moisture. The main points in the discussion are the 

 following : 



The dominating influence of the chemical constitution of soil. 



One of the earliest advocates of the chemical theory was the Austrian, 

 Unger. He directed special attention to the contrast between calcareous 

 and siliceous or slate soils, and he ranged plants in three groups : 



Indifferent to soil, are those plants unaffected by the chemical nature 

 of the substratum. 



^ Petry, 1889. ' Flahault, 1893. ' Magnin, 1893: 



