Whorled Milkweed 
19 
vincing circumstantial evidence that the weed has become es- 
tablished at these points from seed carried on the hoofs or in the 
tails or coats of animals that have been unloaded from the cars. 
A very noticeable case of this kind is the occurrence of a single 
isolated patch of the milkweed at Jay spur on the D. & R. G. 
narrow guage above Ridgway in Ouray County. So far as could 
be determined by a rather careful survey of the Dallas Valley, 
this is the only patch present. The closest known infestation is 
in the Uncompahgre Valley around Colona and Uncompahgre, 
about fifteen miles below Jay spur, and, therefore, the seed could 
not have been carried by water. Many cattle are loaded in th^ 
Colona and Uncompahgre section and shipped up Che narrow 
gauge. Occasionally some of these are unloaded at Jay spur. 
The most obvious explanation of the spread of the milkweed in 
this case is the carrying of the seed by animals in the cars. 
Other places where milkweed occurs under very similar con- 
ditions as stated above are at stockyards near Dolores, Colorado, 
and at Cucharas Junction in Huerfano County. There can be no 
doubt that the milkweed is being carried to new territories by 
this means. 
Animals. — The probable carrying of seed by animals being 
shipped has been noted above in connection with dispersal by rail- 
roads. Since the seed is not fitted with clinging structures it 
is not likely that animals are a very important factor in carry- 
ing milkweed seed, but a very interesting case came under the 
writer’s observation in Archuleta County the past summer. Milk- 
weed occurs in this county along the main sheep driveway to 
the summer range. There is no other infestation in this section 
except in the driveway, where the animals have trampled the 
ground. It is known that the lower winter and spring ranges are 
in bad milkweed areas, and it is probable that in this case the seed 
has been carried in the wool or hoofs of the sheep and trampled 
into the soil. 
Possibility of Dispersal In Crop Seeds. — While no definite cases 
of the establishment of new patches through impure seed 
have come to the attention of this station, the writer can see no 
reason why such has not been the case. There are many grain 
fields in which the milkweed produces seed before the grain is 
cut and the writer has seen bins of grain containing milkweed 
seed. One case has been reported of a man feeding oats contain- 
ing a large quantity of milkweed seed with the death of a horse 
from typical poisoning symptoms as a result. Milkweed seed is 
undoubtedly present in some grain that is harvested in this State 
