96 FARM WEEDS OF CANADA 



rye grass sod. When embedded in moist soil the seeds do not 

 long retain their vitality. 



Hare's-ear Mustard has frequently been introduced into 

 mixed farming districts but does not long give serious trouble 

 where systematic crop rotation is practiced. Sheep seem to 

 like the young succulent plants almost as well as rape and other 

 cultivated species belonging to this family. 



TUMBLING MUSTARD (Sisymbrium allissimum L.). 



Other English names: Tall Sisymbrium, Tumble Mustard. 

 Other Latin names: Sisymbrium sinapistrum Crantz; Sisym- 

 brium pannonicum Jacq. 



Introduced into the Prairie Provinces from central and 

 southern Europe about 1887. Annual and sometimes winter 

 annual; 2 to 4 feet high, stem branching, the lower part and 

 the root-leaves downy and glandular, with a musky odour; 

 upper part of the stem and the much-divided leaves smooth. 

 The young plants form a rosette of soft, pale green, downy leaves, 

 shaped much like those of Common Dandelion. On the flowering 

 plants the leaves change very much in shape from the root up, 

 no two being alike. Flowers pale yellow, 1/3 inch in diameter. 

 Seed pods 2 to 4 inches long, very slender and produced abundant- 

 ly along the branches. Each pod contains about 120 seeds, 

 and a single plant has borne as many as 1,500,000 seeds. When 

 the seeds are ripe the whole head of the plant breaks off and 

 is blown across the prairie, scattering the seeds far and wide. 

 The seeds, as in many "tumbling weeds," are not easily shed 

 from the tough pods; consequently a head of this weed may 

 blow about the prairie for a whole winter, dropping a few seeds 

 at intervals for many miles. 



The seed (Plate 73, fig. 39) is small, 1/25 of an inch long, 

 olive brown or greenish yellow, minutely roughened with muci- 



