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THE FACTORS [Part 1 



■'1 



quantities of definite mineral substances, such as common salt or carbonattl 

 of lime. Mutatis mutandis, the same holds good, but with a greate:' 

 diversity, for plants growing on an organic substratum. 



We found in particular among lime-plants the phenomenon, at firs 

 sio"ht puzzling, that one and the same species in dift'erent localities mad' 

 quite difterent demands as to the chemical nature of the substratum. Th(i 

 same phenomenon also occurs in relation to many parasites. The mistletoi 

 in many districts attacks onl>- the silver-fir, in others only broad-leavec 

 trees. Loranthus europaeus in Bohemia grows only on the oak, in the 

 East on the chestnut also. Puccinia sessilis on Convallaria majalis, P 

 Digraphidis on Polygonatum multiflorum and Maianthemum Convallaria 

 P. Paridis on Paris quadrifolia, are in many regions strictly confined t( 

 their usual hosts; in other regions, however, they grow indiscriminate!} 

 on Convallaria, Polygonatum, Maianthemum, or Paris, and are thus in 

 different as to substratum (Magnus). A similar condition holds good fo 

 many other fungi. There cannot be a doubt but that, as in the case o 

 plants in relation to lime and other mineral salts, here too difterences ii 

 organization come into play, which differences in turn correspond to d: 

 similar requirements as regards the conditions of life. Such changes is 

 organization are not always open to ocular demonstration^ as in many case 

 they are confined to the most minute structure of the protoplasm and ar 

 beyond the reach of our means of observation. There are, however, specie 

 of rust-fungi that in certain stages of their development agree with on 

 another completely, but in other stages distinctly and constantly differ ani 

 are purely ' physiological ' species ; they can be distinguished from on 

 another by no morphological character, and yet show a decidedly specifi 

 character in that they are connected with different host-plants and lack an; 

 power of reciprocal interchange (Eriksson). 



SELECT LITERATURE. 



I. The Physical Properties of the Soil. 



Gain, Ed. I. Action de I'eau du sol sur la vegetation. Revue generate de botaniqu 



Tome VII. 1S95. 

 -— II. Recherches sur le role ph3^siologique de Teau dans la vegetation, Annalt 



des sciences naturelles. ;« serie. Tome XX. 1895. 

 Hoflfniann, H. Untersuchungen zur Klima- und Bodenkunde mit Riicksicht auf di 



Vegetation. Botanische Zeitung. Bd, XXIII. 1865. Beilage, 

 Mayer, Ad. Die Bodenkunde. 4. Auflage. 1S95.. (Lehrb. der Agriculturchemii 



Zweiter Theil. 1. Abth.). 

 Sachs, J. V. Ueber den Einfluss der chemischen und phj'sikalischen Beschaffenhe 



des Bodens auf die Transpiration der Pflanzen. Landw. Versuchsstationei 



1859. (Ges. Abhandl. Bd, I. p. 417.) 

 Thurmann, J. Essai de phytostatique appliquee a la chaine du Jura. Berne, iS49' 



