THE GENERAL PROPERTIES OF POISONS 263 



nickel, cobalt, cadmium, and mercury, whereas the plant can withstand 

 sulphate of copper in high concentrations without previous accommodation. 

 Germination and growth are, however, slower on solutions of copper when 

 normal spores are used than when the latter are taken from plants grown 

 in the presence of large amounts of copper. 



In all these cases we are dealing with a physiological response to 

 increased demands, which result here in an increased resistant power. 

 This special power is gradually lost in the course of a few generations, 

 as the after-effect of the previous treatment dies away. It might, however, 

 be possible to raise varieties in which the special resistant power became 

 a permanent hereditary character 1 . 



A plant resistant to one poison. is not necessarily resistant to all, and 

 hence the accommodation to a particular poison presumably takes place 

 in regard to that poison only. It is, however, uncertain whether this 

 acquired immunity extends to groups of allied substances. In the case 

 of fungi it appears that a plant can accommodate itself to one metallic 

 poison without the poisonous action of others being diminished. Similarly 

 the accommodation of animals by breeding to ricin does not affect the 

 poisonous action of abrin upon them 2 . 



Owing to the influence of the present and previous conditions, the 

 maximal and ultra-maximal concentrations for different poisons cannot be 

 precisely fixed even in a particular species. Further, the maximum 

 concentration will depend upon whether the cessation of growth or actual 

 death is taken as an indication of fatal action. 



Poisonous action plays an important part in the competition between 

 micro-organisms, and also in the injury of host-plants by parasites. Green 

 plants, however, are usually able to avoid the action of poisons, owing to 

 the absorbent properties of the soil, to the continued removal of the 

 carbon dioxide they produce, and to the precipitation and deposition of 

 poisonous substances in dying tissues, or in living ones in an innocuous 

 form 3 . The gases from volcanoes, factories, and gas-burners or gas-works, 

 and the liquids from chemical sewage and dye works, as well as salt 

 water and the like, may injure severely or kill plants reached by them 4 . 



Apart from its physiological aspect we are not concerned with Toxico- 

 logy, the older literature of which is given by de Candolle 5 , Treviranus 6 , and 



1 Possibly some of the varieties of yeast have acquired an enhanced resistance to alcohol. 



2 Robert, Lehrb. der Intoxicationen, 1893, p. 151 ; Loew, System d. Giftwirkungen, 1893, p. 80. 



3 Vol. I, Sect. 28; Tschirch, Das Kupfer, 1893, p. 13; Otto, Landw. Jahrb., 1896, Bd. xxv, 

 p. 1,007. 



4 Frank, Krankheiten d. Pflanzen, 1895., 2. Aufl., Bd. I, p. 313 ; Sorauer, Bot. Centralbl., 1899, 

 Bd. LXXX, p. 50. On the resistance of seeds and spores to digestion cf. Ludwig, Biol. d. Pflanzen, 

 1895, p. 365 ; Huth, Bot. Jahresb., 1888, Bd. I, p. 566. 



6 De Candolle, Physiologie vegetale, 1832, T. m, p. 1,324. 

 e Treviranus, Pflanzenphysiol., 1838, Bd. II, p. 721. 



