46 
BULLETIN 191, U. S. DEPARTMENT OF AGRICULTURE. 
tansy mustard, for example, have averaged more than 70 per cent, 
considerably exceeding the highest average- seed-test records of per- 
ennial species. Generally, the seed of the more aggressive annuals 
are plump and well filled with reserve food. Another distinct ad- 
vantage observed in the case of the seed of the ruderal weed species A 
Goosefoot or lainb's-quarters 
( Oil enopodhi m (OVu m ) . 
Fig. 17.- — Plants characteristic of the first or early weed stage 
Slender-leaved coilomia 
(CoUomia linearis). 
is their ability to germinate under conditions of temperature ad- 
verse to most plants. Seed of Douglas knotweed, tansy mustard, and 
tar weed, for instance, have been observed to sprout when the maxi- 
mum diurnal temperature has not exceeded 50° Fahrenheit, the 
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