CHAPTER XX. 
WEEDS 
310. What isa weed? The term weed is not a botanical 
one but is a common word for the conspicuous troublesome 
or injurious plants. It is not customary to apply the name 
weed to lower forms of plant life, such as bacteria and fungi, 
even though they may be extremely harmful to field and 
garden crops, orchards, or forests. Most weeds are flower- 
ing plants, but horsetails and a few ferns (as the sensitive 
fern, fig. 216) are sometimes troublesome enough to be classed 
in the list. 
The same plant may be counted a weed in one place and 
not in another. The sensitive plant, not uncommon as a curi- 
osity in our greenhouses, is a troublesome weed over immense 
areas in the tropics. Wild carrots, of the same species as the 
cultivated ones, are a nuisance in New England mowing lands 
and are rapidly extending westward; field garlic, melilot, horse- 
radish, tansy, oxeye daisy, and orange hawkweed, or “ paint- 
brush,” were all introduced as valued garden plants, afterwards 
becoming noxious weeds. 
311. Why weeds succeed. The characteristics which enable 
weeds to flourish where farm and garden crops need care to 
enable them to grow are too numerous to be stated and ex- 
plained at length in a very elementary book. Some of the 
important characteristics which distinguish most weeds are: 
1. Great reproductive power. 
2. Capacity for rapid growth, which enables them to shade 
and destroy other plants. 
3. Ability to resist drought, shading, frost, and plant 
diseases. 
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