CHAPTER XXI 
THE STRUGGLE FOR EXISTENCE AND THE SURVIVAL 
OF THE FITTEST! 
245. Weeds. — Any flowering plant which is trouble- 
some to the farmer or gardener is commonly known as 
a weed. Though such plants are annoying from their 
tendency to crowd out others useful to man, they are of 
extreme interest to the botanist on account of this very 
hardiness. The principal characteristics of the most suc- 
cessful weeds are their ability to live in a variety of soils 
and exposures, their rapid growth, resistance to frost, 
drought, and dust, their unfitness for the food of most of 
the larger animals, in many cases their capacity to accom- 
plish sel-pollination in default of cross-pollination, and 
their ability to produce many seeds and to secure their 
wide dispersal. Not every weed combines all of these 
characteristics. For instance, the velvet-leaf or butter- 
print,? common in cornfields, is very easily destroyed by 
frost; the pigweed and purslane are greedily eaten by 
pigs, and the ragweed by some horses. The horse-radish 
does not usually produce any seeds. 
It is a curious fact that many plants which have tnally 
proved to be noxious weeds have been purposely introduced 
into the country. The fuller’s teasel, melilot, horse-radish, 
1 See Darwin’s Origin of Species, Chapters HI and IV. 
2 Abutilon Theophrasti. 
200 
