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field. In considering the matter, suspicion fell at once on the cocklehurs, 
xanthium canadense. The experiment field was very foul with this pest when 
the station secured it, and it was noticed that the soil secured the first year 
showed more toxic effect than that secured the second year, either in the 
greenhouse or in the field. This might have been due to the clean culture 
given the field as soon as it came under the management of the station. 
Henry Wallace^ reports that the idea of the toxic action of weeds came to 
him in a conversation with the celebrated Sir John B. Lawes. When looking 
over his famous experimental plots at Rothamstead, England, he showed Mr. 
Wallace a field of wheat that had been in continuous cultivation without ma- 
nuring for forty-five years, with a gradual decreasing yield. It had, however, 
been carefully hand weeded; and Sir John made this remark: “We must get 
rid of weeds. Weeds poison the land.” 
That the bur is poisonous to animals is known. Mayo® states that the com- 
mon cocklebur seems to cause poison only in its early two-leaf stage, when the 
cotyledons are well developed. Animals never eat the unsprouted burs for 
very evident reasons. He mentions cases where it seems that the burs had 
killed quite a number of hogs. Nobody has isolated and studied this poison. 
The poisonous principle of another species of cocklebur, X. strumarium, was 
investigated by A. Zander^, a German investigator, in 1881. He isolated the 
poisonous principle and named it zanthostrumarin. No formula or classifica- 
tion v/as given for the poison. If the cocklebur contains a substance that is 
poisonous to animals, why should not this substance he poisonous to plants? 
The living cells of animals and plants are very similar and respond to stimuli 
in nearly the same manner. They are affected by the same poisons and differ 
only in degree of susceptibility. 
With a view of investigating the production of a toxin in the soil by cockle- 
burs, five samples of soil were secured from the field in October, 1906, so that 
soil which had suffered different treatments could be compared. These samples 
were pulverized as soon as they reached the laboratory and placed in closed 
cans to prevent drying, in order to keep them as near field condition as pos- 
sible. 
A sample was taken from plot 101 to be as near as possible like the samples 
secured the previous year. This w^as in clover at the time the sample was 
secured, and had been in oats and clover the year previous. The clover was 
a thin stand. 
Samples were secured from plots 113 and 213. These were new plots added 
in the spring of 1906. Plot 113 was sown to cowpeas in June but they had 
proved a failure. Plot 213 was in oats and clover. The oats yielded 7.5 bushels 
per acre and the clover was a failure. They both raised a very light crop of 
beans the previous year, w^ere left rough and lumpy, and were very foul with 
cocklehurs and horse nettles. 
A sample was secured from plot 208. This had the same crop and treatment 
during 1906 as 213, but the oats yielded 23.1 bushels. The clover was practi- 
cally a failure. The crop in 1905 was corn which had been kept free from 
weeds. 
-See Wallaces’ Farmer of June 7, 1907. 
3Proc. Am. Vet. Med, Assn., 1902, p. 194, 
^Dictionary of the Active Principle of Plants. Solin. 
