COCKLEBURS AS POISONOUS PLANTS 
19 
ARE THE POISONOUS properties of the cotyledons derived from the 
SEEDS? 
Since the seeds are by weight much more poisonous than the young 
plants, and as the plants, early in their growth, lose their toxic prop- 
erties, the question has arisen whether the young plants derive their 
toxicity solely or largely from the seeds. If the plants contain sim- 
ply the toxic material from the seeds, animals should be poisoned by 
a number of plants equal to the number of seeds which produce a 
poisonous effect. Counts were made in 5 experimental feedings to 
pigs of seeds, in 11 feedings of the whole plant in young cotyledon 
stage, and in 6 feedings of cotyledons. 
The results were as shown in Table 4 : 
Table 4. — Number of seeds, plants, and cotyledons producing toxic and nontoxic 
effects to pigs 
Part of plant 
Number of 
seeds per 
hundred- 
weight of 
animal 
Seeds . 
Minimum 
Fatal 
2,200 
1,800 
900 
Whole plant 
Minimum 
Maximum .._ 
Fatal 
Nontoxic. _ 
1,200 
Toxic 
1,600 
1,600 
Maximum _. . . 
Nontoxic. 
Since in the case of the seeds no effect was produced by 1,800, it 
may be assumed that 2,200 is not only the lethal dose but is not far 
from the toxic dose. 
Of the whole plant, as there were 11 feedings, 9 of which were 
between 900 and 1,200, it seems probable that 900 is very close to the 
minimum toxic and lethal dose. 
With the pairs of cotyledons, 1,600 produced symptoms and in 
another case the same number had no effect, so here, too, the dosage 
must be close to the minimum. While too much reliance must not 
be placed on the comparatively small number of experiments, never- 
theless the results have some significance, but do not show the ex- 
pected correlation. On the contrary, considering numbers only, the 
whole plant is most toxic, the cotyledons next, and the seeds least 
of all, the proportionate toxic doses being 9, 16, and 22. As the 
writers have no knowledge of the chemistry of the plant, it is im- 
possible to explain this fact. It is possible, of course, that the toxic 
substance is not actually greater in the plant, but is in a more avail- 
able form, but it is also possible that a greater quantity is secreted 
in the plant. These figures also show quite clearly that the cotyle- 
dons do not contain all the toxic substance, as it takes 1,600 cotyledons 
to equal the effect of 900 whole plants. 
MECHANICAL INJURY BY BURS 
As stated in the historical resume, some writers claim that the burs 
injure animals either by irritation caused by the spines, or by ob- 
struction of parts of the alimentary canal, or by both. There was 
little evidence in the experiments made by the writers either in sup- 
