22 
Colorado Experiment Station 
that this reduction in the number that live over combined with 
the number that germinate in the fall so reduce the number left 
the following spring that the seedlings which do come up are so 
few as to easily escape detection. 
When it is taken into consideration that it has been estimated 
that a single exceptionally large plant of milkweed as shown in 
Fig. 16, is capable of producing 10,000 to 13,000 seeds and that 
90 to 98 per cent, of these are viable, it is readily seen that rapid 
spreading of the plant depends only on the efficiency of the 
agents of dispersal as discussed in the foregoing pages. 
CONDITIONS UNDER WHICH POISONING OCCURS 
The general statement that stock do not like poisonous plants 
but will eat any other kind of forage in preference to them, is es- 
pecially true of whorled milkweed. Numerous cases have been 
observed of cattle being grazed in pastures where milkweed oc- 
curs without there being any losses or any symptoms of poison- 
Fi&. 16 — An exceptionally large milkweed 
plant estimated to have 13,000 seeds. 
ing, but in every case it has been found that the milkweed grows 
up and goes to seed, although all other forage may be eaten close 
