158 NATURE STUDY AND AGRICULTURE 
2. Many of them, as the thistle, dandelion, and tumble- 
weeds, have special means of scattering their seeds far and 
wide. 
3. Many weeds are very prolific in the production of seeds. 
The Russian thistle will easily yield 20,000 seeds, and a single 
tumbling mustard has been known to produce 1,500,000 
seeds. 
4. Many of them, like the proverbial cat with nine lives, 
are exceedingly hard to kill. If we cut a purslane into a dozen 
pieces and leave them on the ground, each piece may take 
root and form a new plant, so that we make twelve weeds 
grow where only one grew before. Quack grass and Canada 
thistle are other examples of the great tenacity of life among 
weeds. 
5. The ripening of the seeds is well timed to suit their 
particular method of propagation. Cockle ripens just in 
time to be harvested with wheat, and false flax with culti- 
vated flax. Wild oats and mustard ripen before our grains, 
so that the seeds fall to the ground before they can be gath- 
ered up by the harvester, — self-seeding being their usual 
method of reaching the seed bed. 
Native and Introduced Weeds. — Nearly all our weeds 
have been associated with cultivated crops for centuries 
and are the “survival of the fittest” for their particular 
mode of life. They have been introduced with our field 
and garden seeds, being among the evils that follow civiliza- 
tion, like rats and mice. The native plants of our prairies 
are generally lacking in the necessary attributes, and there- 
fore do not make efficient weeds. Of the 35 or 40 species 
named in this chapter, the marsh elder, great ragweed, and 
wavy-leaved thistle are the principal ones that are natives 
of the northwestern states which they now infest. 
