12 FARM WEEDS OF CANADA 



such weeds as the mustards, cockles and pigweeds, when fresh, 

 possess a protective coat that is almost impervious to water. 

 As a rule, the seeds of such weeds retain their vitality for a 

 number of years and germinate only when the hard seed coat has 

 become disintegrated by continued exposure to the action of 

 the sun, air or other climatic or soil conditions. Thus are such 

 weeds naturally distributed in time. 



b. Weeds distributed in space are those the seeds of which, 

 when mature, are provided with means for natural distribution 

 by wind or other agencies. The thistles, hawkweeds and dande- 

 lions are examples of weeds distributed in space. The seeds of 

 such weeds, as a rule, do not retain their vitality for more than 

 a few years. 



WEED SEEDS IN THE SOIL. 



The ability of the seeds of many species of plants to retain 

 their vitality when embedded in the soil for a period of years is 

 one of the principal factors which brings them within the category 

 of noxious weeds. 



It is commonly asserted by farmers that seeds of several 

 species of the Mustard and other families will retain their vitality 

 for an indefinite period. The apparent absence of mustard in 

 old pastures, roadways or lands left waste during many years, 

 and the re-appearance of the plant when the land is brought 

 under cultivation, forms the usual evidence to bear out such 

 assertions. An examination of permanent pasture or waste 

 lands that are known to have been polluted with mustard will, 

 however, show occasional inconspicuous plants that give promise 

 of ripening a few seeds. 



Duval, of Washington, D.C., in December, 1902, buried 

 112 different kinds of seeds in clay soil in earthen pots, to depths 

 of six, eighteen and thirty-six inches, and compared their vitality 

 with control samples kept in proper storage. When dug up 

 in November, 1903, practically all the seeds of cultivated plants 

 were decayed, many of them having first germinated, even at 



