246 PASTORAL AND AGRICULTURAL BOTANY 



Lines of Travel. The lines of travel of weeds are of interest. The 

 chicory was introduced into the United States near Dorchester, Mass. 

 in 1875. It is a common weed in western Long Island, eastern Pennsyl- 

 vania, although of recent introduction there, and in the northern states. 

 The water hyacinth (Eichornia crassipes) was introduced into the St. 

 Johns' River in Florida in 1890. It has spread southward and westward 

 through the state along the river courses, so as to choke them and impede 

 navigation. The cardoon (Cynara cardunculus) introduced into Argen- 

 tina from Europe covers the pampas for miles. The introduced redtop 

 follows the abandoned wagon tracks across the otherwise unbroken prairie 

 for miles. 



SPECIAL WEED EXAMPLES 



Goose-Grass (Eleusim indica). This coarse grass came to us from 

 India and seems to be thoroughly domesticated. It grows from clustered, 

 fibrous roots and forms spikes in digitate clusters at the end of the stalk. 

 It grows as a weed in yards and waste places. It can be controlled in 

 lawns by squirting a few drops of crude carbolic acid into the heart of a 

 tuft with a common machine oil-can, which treatment ought to kill it. 



Field Sorrel (Rumex a^etosella). The sheep sorrel has extensively 

 creeping rootstocks with tufts of feeding roots. The radicle leaves are 

 halberd-shaped and from their midst arises the flower stalk bearing male 

 and female fldwers on separate plants (duecious). Sorrel can be controlled 

 by cultivating the soil and adding lime to correct its acidity (Fig. 102). 



Russian Thistle (Salsola kali var. tenuifolia). This chenopodiaceous 

 plant was introduced into the Dakotas and Minnesota in flax seed from 

 Russia. It is a pernicious weed in grain fields and spreads itself as a 

 tumble weed, scattering its seed, as it rolls over the ground blown about 

 by the wind (Fig. 100). It can be controlled by sowing only clean seed and 

 in cutting down the weed before it is allowed to seed. It then dies a 

 natural death. 



Chickweed (Cerastium arvense). This is a pestiferous weed in alfalfa 

 fields in eastern Pennsylvania and elsewhere. It is a winter annual with 

 densely tufted stems, opposite, linear-oblong leaves and white flowers 

 with bifid petals. It is difficult to eradicate unless a rotation of crops is 

 practised, the alfalfa, or grass crops invaded by chickweed being alter- 

 nated with hoed, or cultivated crops. 



