I04 



THE FACTORS 



[Part 1 



hoii'cvcr, change with the arca'^. In one area the silica-form, in anothet 

 the lime-form, is better adapted to local conditions, whilst in a third arei 

 both forms may be able to maintain themselves in the struggle for existence 

 Accordingly, one and the ' same species is calciphobons in the first area 

 calciphilons in the second, and indifferent in the third. 



An instructive example of the dissimilar physiological properties o 

 the lime-form and the silica-form of the same species of plant is affordec 

 by Pinus uncinata. This pine in its lime-form, at least in Switzerlant 

 and Bavaria, prefers dry gravel, whilst in its silica-form it avoids stonj 



dry spots and occurs onl; 

 on moorlands. In othe 

 regions, with a different cli 

 mate, probably both form 

 would behave in anothe 

 manner. 



Nageli and Christ hav 

 proved, in the case 

 closely allied species 

 Gentiana, Achillea, an 

 Rhododendron:that closel 

 allied plant-organisms be 

 have very differently as re 

 gards the chemical qualit 

 of their substratum. Thu 

 in Switzerland, Gentian 

 acaulis is calciphilous, wher 

 asthecloselyallied Gentian 

 excisa (I'ig. 54), which 

 usually considered as 

 mere variety of the forme 

 is calciphobous ; neither 1 

 them is quite exclusiv 

 in its choice. Similar pairs, although less like, are Achillea atrata an 

 A. moschata (Fig. 55), Rhododendron hirsutum and R. ferrugineun 

 Androsace pubescens and A. glacialis, Juncus Hostii and J. trifidu 

 of which pairs the species first named is calciphilous. Kerner has drawi 

 up a long list of such parallel species-. I 



The parallel forms are usually confined to their respective soils in tl: 

 regions where both occur, but are indifferent as regards their choice ( 

 soil, wherever one of them is absent. Nageli ■' has ingeniously indicate 



' The remarkably great susceptibility of a plant-organism to insignificant external it 

 fluences foliows from Wettstein's brilliant researches on Gentiana and Euphrasia. 

 " Kerner, I. s Nageli, op. cit. 



Fig. 54. I. Gentiana excisa, Presl. Calciphobous. 2. Gen- 

 tiana acaulis, L. ex p. Calciphilous. Two-thirds of natural 

 size. 



