56 INFLUENCE OF CHEMICALS 



A few of the alkaloids are capable of exerting a toxic effect 

 upon plants by direct action. In general however, the alkaloids 

 are exceedingly divergent in their action ; these substances are 

 nitrogenous, basic and very complex. It is supposed that their 

 deleterious influence is due to the union of the bases with the 

 active proteins of the cell, thus setting up most serious disturb- 

 ances. 1 



88. Toxic Action of Alkaloids, Place hairs of Tradescantia or 

 filaments of Spirogyra in . I per-cent. and 3 per-cent. solutions of 

 caffeine on glass slips, and note changes in the cell as seen with a 

 magnification of 4-500 diameters. Make similar tests with cocaine. 



Dissolve i part of sulphate of quinia in one thousand parts of 

 distilled water, and test the influence of this solution upon motile 

 zoospores and hairs with streaming movements of the protoplasm, 



89. Self-poisoning. The alkaloids and other poisonous sub- 

 stances produced by the metabolic action of the plant may serve 

 the incidental purpose of protecting the plant from the ravages of 

 grazing animals, but they are usually by-products which the or- 

 ganism translocates to some portion of the body which is cast off, 

 or they are united with other substances to form insoluble or in- 

 nocuous compounds. Disturbance of this action by the plant 

 may result in pathological conditions. Furthermore, substances 

 not ordinarily known as poisons may act as such by their destruc- 

 tive action upon essential constituents of specialized cells. An 

 example of this is to be found in the increased production of oxi~ 

 dase in the leaves of the tobacco plant, in which the increased 

 enzyme is not kept to its usual function, but attacks the chloroplasts 

 and disintegrates the chlorophyl, inducing a pathological condition 

 of the leaf. Doubtless many other pathological phenomena are 

 also due to a lack of proper automatic control of metabolic prod- 

 ucts owing to unusual cultural conditions (See oxidases). 



90. Acclimatization to Chemical Action, A summary of the 

 results obtained in the previous experiments shows that the proto- 

 plasm of different organisms has a different capacity for resistance 



1 Loew, O. Ein natUrliches System der Gift- Wirkungen. 1893. 



