14 PASTORAL AND AGRICULTURAL BOTANY 



6. Influence of Soil. The soil has considerable influence on the 

 amount of poisonous substance developed in plants. The trailing, 

 yellowish-green form of poison ivy, Rhus radicans, found on the coastal 

 sand dunes is less virulent than the climbing form found inland. This 

 difference in the poisonous properties is to be attributed to growth on the 

 barren sand of the sea coast. 



7. Influence of Cultivation. Cultivation has a marked influence. 

 In general, wild poisonous plants have larger amounts of alkaloids and 

 glucosides than the same species when cultivated, although this does not 

 always hold true. The wild forms of the Lima bean, Phaseolus lunatus, 

 contains much more HCN than the cultivated forms. 



8. Variation in Amount of Poison. The amount of poison contained 

 in plants of the same species depend upon, the race or variety of that 

 particular species utilized for the extraction of the drug, or poison. Blyth 

 records the following percentages of nicotin in various tobaccos as given by 

 Cox (Pharm. Journ., Jan. 20, 1894). Syrian leaves (a) .612 per cent.; 

 Syrian leaves (b) 1.093 P er cent.; Gold Flake (Virginia) 2.501 per cent.; 

 Navy Cut (light colored) 3.640 per cent.; Best Shag (b) 5.000 per cent.: 

 Algerian tobacco (a) 8.813 P er cent. 



9. Weather and Poisoning. The state of the weather has consider- 

 able effect on the number of cases of poisoning among cattle on the free 

 range. The death camas, Zygadenus venenosus, found in California, is 

 a case in point. The bulbs of this plant are dangerous only after rains, 

 since at other times, it is almost impossible for sheep to pull them out 

 of the ground. Many serious cases of stock poisoning have occurred after 

 late spring and early autumn snow storms, because the grasses and other 

 low plants are covered with snow and only the taller plants remained 

 visible and then were poisonous. 



10. Seasonal Distribution of Cases of Poisoning. There are more 

 cases of poisoning of stock in certain seasons of the year than others. 

 Laurel, Kalmia latifolia, is more likely to be browsed in winter and 

 early, spring, because of its attractive, bright green color, when other 

 plants are dormant. Cattle are more subject to loco disease in the 

 spring, because the loco weeds become green early in the spring and are 

 browsed upon by animals while the other green herbage is scarce at this 

 time of the year. 



1 1. Specific Differences of Animal Susceptibility . The different kinds 

 of live stock are affected quite differently by poisonous plants. Human 



