CHAPTER XXI. 
The Struggle for Existence and the Survival of the 
Fittest. 
238. Weeds. — Any flowering plant which is troublesome 
to the farmer or gardener is commonly known as a weed. 
Though such plants are so 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 prin- 
cipal characteristics of the most successful 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 accomplish self-fertilization, in default of 
eross-fertilization, and their ability to produce many seeds 
and to secure their wide dispersal. Not every weed com- 
bines all of these characteristics. For instance, the velvet- 
leaf or butter-print? common in corn-fields, 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 finally 
proved to be noxious weeds have been purposely introduced 
into the country. The fuller’s teasel, melilot, horseradish, 
wild carrot, wild parsnip, tansy, ox-eye daisy, and field-garlic 
are only a few of the many examples of very troublesome 
weeds which were at first planted for use or for ornament. 
1 See Darwin’s Origin of Species, Chapters III and IV. 
2 Abutilon Avicennez. 
