CHAPTER XX. 

 WEEDS 



310. What is a 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. 



