along roadsides. The petioles and peduncles of Cardoon (Cynara 

 cardunculus, Compositae) are prized as a food item by people 

 of Mediterranean ancestry; this attractive thistle has escaped 

 from gardens and has become locally established on the hills 

 around San Francisco Bay. This is perhaps also the explanation 

 for the presence of Sweet Fennel or Finocchio {Foeniculum vul- 

 gare, Umbelliferae), which is common in waste places of central 

 and southern California. The broad definition of a weed also can 

 include trees such as Blue Gum (Eucalyptus globulus, Myrtaceae), 

 a tree which is maintaining itself in some areas of California 

 where it was introduced as an ornamental and for possible lumber 

 purposes. Several species of tamarisk (Tamarix spp., Tamarica- 

 ceae) have become established along water courses in desert areas, 

 although the trees were originally introduced as ornamentals or 

 as windbreaks. Perhaps one of the most pernicious weeds in Cal- 

 ifornia is Johnson Grass (Sorghum halepense, Gramineae), origi- 

 nally grown as a forage grass. It has since become established 

 widely as a troublesome and economically expensive pest of field 

 crops. The list of such weeds that have escaped from cultivation 

 is an extensive one. 



It is probable that the majority of weeds in California have re- 

 sulted from accidental introductions of seeds rather than from 

 intentional introductions. In former days, much of the seed of 

 various field or garden crops planted in California originated from 

 Old World areas and was contaminated with a number of weed 

 seeds from these regions. Planting of the seeds of these crop or 

 ornamental plants resulted in accidental planting of weeds as 

 well. In addition, in former years anumber of weeds have been in- 

 troduced into the American west as contaminants of wool im- 

 ported from the British Isles, South America, or Australia. Such 

 weeds initially became established in the vicinity of woollen 

 mills, but many of them spread rapidly from these sites of intro- 

 duction. Another means of weed introduction in the nineteenth 

 and early twentieth century was via ballast. In former times 

 ships visiting the west coast of North America carried ballast in 

 the form of soil or rocks that had been put on board in various 

 foreign ports. Ballast was emptied from the ships at dockside, 

 and a number of unusual and interesting botanical aliens have 



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