84 WEEDS OF THE FARM AND GARDEN 



there are tropical plants which have become thoroughly 

 naturalized, as Amaranthus retroflexus, A. albus, A. spino- 

 sus, Abutilon Theophrasti and Sida spinosa. Within the 

 memory of the present generation Indian mallow has 

 been naturalized in western Wisconsin ; Argemone mex- 

 icana in a comparatively short time has found its way 

 into Kansas, Iowa and Illinois. Cardiospennum Halica- 

 cabum of the southwest is common in Illinois opposite St. 

 Louis. 



Of our early weeds reliable information is often want- 

 ing, although in some cases the history is well known. 

 Prickly lettuce (Lactuca Scariola) made its appearance 

 in eastern Massachusetts first in 1863, but is now found 

 in mlany states of the Union, growing like a native plant. 

 Mention of this weed was made by Professor Arthur in an 

 early catalogue, but it either failed to establish itself or it 

 escaped the notice of botanists. In Europe, we have 

 reliable information concerning the spreading of a num- 

 ber of weeds. Water weed (Elodea canadensis), a most 

 harmless water plant in North America, first appeared 

 in Ireland in 1838; in 1846 it was recorded in Scotland; 

 in 1860 it was observed on the continent; in 1862, it be- 

 came generally distributed. Dr. Webber thinks that the 

 gradual lessening of this weed in Europe may have been 

 due to some natural enemy. 



The water hyacinth (Eichornia crassipes) has become 

 a serious menace to navigation in Florida. This plant, 

 which is a native to South America, has long been culti- 

 vated in northern greenhouses. Dr. Webber, who made 

 quite an extensive study of this weed, states that it was 

 probably introduced into the St. John's river about 1890, 

 about four miles above Palatka, where it was grown in 

 a pond. The pond was cleared and the material thrown 

 into the river and from thence it spread to other streams, 

 having been scattered by boats. It became abundant in 

 1894, having been carried up the Ocklawaha River, from 



