THE PRODUCTION OF POISON IN PLANTS 83 



poisonous substance apparently being broken up to serve as a nourishing material 

 for the growth of the plants. 



Cornevin * in his work upon poisonous plants says : In one group "the poison- 

 ous substance does not exist in the plants themselves, but, in some parts or 

 tissue, elements are present which are not really poisonous in themselves but 

 become so when the parts or tissues come in contact with one another. An 

 example is seen in the glucoside amygdalin which in contact with emulsin forms 

 hydrocyanic acid." 



The activity of vegetable poisons may depend upon the age of the plant 

 producing them. No definite rule can be established in regard to the age at 

 which a plant produces its poisonous substance. Sometimes a younger plant is 

 more actively poisonous than when older, sometimes, also, the poison is stored 

 in certain tissues. 



Poisonous principles are found in various parts of the plant, such as the 

 root, stem, flowers, fruit, leaves, bark, tubers, seed and bulbs. 



In many aerial parts of plants the poisonous substances are more ephem- 

 eral than they are in organs of the plant that serve as store houses of food. 



Cornevin says : 



It sometimes happens that the subterranean part only is poisonous as in Atractylis gum- 

 mifera. This is true, also, of the common European Violet. On the other hand, when sub- 

 terranean organs of certain plants come in contact with the light a poisonous substance may 

 be produced. This is true of the tuber of potato which when green is poisonous. Poisonous 

 substances are elaborated both in evergreen and deciduous leaves; no rule of comparison has, 

 however, been established. 



Certain variations of the plant are dependent upon its environment, certain conditions of 

 which play an important part especially in the elaboration of poisonous substances. 



These conditions are light, heat, season, climate, soil, culture and fertility. 



LIGHT. It is a well knewn fact that light seriously interferes with the 

 growth of parasitic fungi and bacteria so that pathogenic species may become 

 quite harmless when placed in direct sunlight. The poison atractylin is formed 

 only in darkness, on the other hand solanin is formed only in the light, as in 

 the case of the green potato. 



HEAT. Cornevin says : 



The action of heat upon plants should be considered with that of light, of the seasonal 

 variation, and of climate, and not as an isolated cause. When it is prolonged it induces dessi- 

 cation of the plant and as a consequence evaporation follows and destruction of the poison when 

 it is volatile. This result is produced in some Ranunculaceae, Chenopodiaceae, etc. 



Moist heat, that is boiling, conduces to the same result in some poisons. Three-seeded 

 mercury (Mercurialis annua) becomes inoffensive when it has been submitted to the action of 

 heat, because of the volatilization of its toxic substance mercurialin. 



SEASONS. Seasons cause considerable variation in the poisonous material 

 produced in plants, the amount of poison contained often varying with the ad- 

 vance of the season. In aconite the poison, at first contained in the leafy or- 

 gans becomes concentrated little by little in the seed. 



The time of the year may have an important bearing upon the amount of 

 poisonous material found in the plant. According to Prof. Hedrick the Cow- 

 bane or Musquash root (Cicuta vagans) of the west is much more toxic in the 

 fall, winter, and spring, than in the summer, and this is partially confirmed by 

 an experiment conducted with our common Cowbane {Cicuta maculata}- It is 

 also well known that the mature bulbs of Colchicum contains a much larger 

 amount of the toxic substances than the growing bulbs and that for medicinal 



l Des plantes veneneuses et des empoisonnements qu'elles deterrminent, 524. Paris, 1893. 



