270 THE POWER OF RESISTANCE TO EXTREMES 



and a salt produced which could readily diosmose away. Phenols and 

 other poisons are presumably often converted into exosmosing innocuous 

 compounds l . Similarly the physiological combustion of alcohol results 

 in the production of products which are either innocuous (water) or can 

 readily diosmose away (carbon dioxide). 



Although a plant may avoid the effects due to the presence of an 

 acid by a corresponding production of alkali, it does not always follow 

 that a poison will be overcome by the formation of an antagonistic one. 

 Nor is accommodation necessarily the result of an increased production of 

 an antitoxin 2 , of which in fact there can be no question when a plant 

 becomes accommodated to high temperatures, or to concentrated solutions 

 of an indifferent substance. The actual origin of these alterations is as 

 little known as that of the changes which occur during the normal progress 

 of development. 



In addition to the means of withstanding poisons already mentioned, 

 a few free-swimming forms have a power of perception and response which 

 enables them to flee from particular poisonous substances such as acids and 

 alkalies 3 . Non-motile organisms, however, absorb almost all poisons when 

 presented in suitable form, although Penicillium behaves exceptionally in 

 this respect towards copper salts. 



Single submaximal doses of poison usually exert an effect which slowly 

 increases to a maximum and then dies away again. If the plant is, however, 

 in permanent contact with a submaximal concentration of poison, a state of 

 equilibrium is ultimately reached, which persists as long as the conditions 

 are unaltered. The protoplast then contains a constant percentage of 

 poison, independently of whether the poison is accumulated within the cell 

 or not. This constancy is the result of the interaction of various affinities 

 and other factors, and is indeed only maintained by perpetual change, 

 when the protoplast continually removes or destroys the poison as it 

 penetrates. If the activity of repair is slight, and if the poisonous action is 

 increased by the accumulation of the poison, then in time extremely dilute 

 solutions of poison may prove fatal, as for example when plants of 

 Spirogyra are submerged in large quantities of water containing the 

 merest trace of copper. The maximum and ultra-maximum for a poison 

 are determined by observing the concentration in which the plant or cell 

 can continue to exist, and that in which it ultimately dies. In this way the 

 relative intensities of two poisons can be compared, and also the relative 

 resistance of two different cells. Such determinations have more scientific 

 value than estimations of the smallest dose of poison required to kill a 



1 As regards animals cf. Kunkel, Toxicologie, 1899, PP- IO > 39 1 - 



2 On toxins and protective substances see the summary by Oppenheim, Biol. Centralbl., 1899, 

 Bd. xix, p. 799. 



3 Pfeffer, Unters. a. d. Bot. Inst. zu Tubingen, 1886, Bd. II, p. 627. 



