'30 THE MONTANA EXPERIMENT STATION. 



ripening and prompt shelling of the fruit, its black hull (flowering 

 glume), hairy at base and with a twisted awn and in its smaller 

 and lighter seed. Its fecundity, rapid growth and self-seeding 

 qualities soon enable it to take a field sown continuously 

 in any kind of grain and the persistent vitalit\^ of its seed in the 

 soil makes it difficult to eradicate. It can best be combatted by 

 sowing down infested fields in clover, timothy or alfalfa, or by 

 close pasturage by sheep for several years of such fields, planted in 

 some annual grain suitable for forage. There is a general belief 

 among farmers that the wild oat often originates as a degenerate 

 form of the cultivated variety with which it seems to intergrade, 

 and, while it is propagated in general fronuits own seed, its gen- 

 eral occurrence and abundance in fields sown in oats throughout 

 the arid region seems to favor the idea of such reversion. More- 

 over, the cultivated oat is supposed to have been derived from the 

 wild species, and several authenticated instances are known of the 

 production of the tame varieties from the wild form b\ r cultivation 

 and reversion under suitable climatic conditions is much more 

 probable, as i$ certainly the case w T ith many other cultivated 

 plants, such as the radish, carrot, turnip, mustard and parsnip, 

 which in many places readily revert to the wild form and become 

 troublesome weeds. [Fig. 3.] 



19. BRASSICA CAMPESTRIS L. Kale; Wild Turnip. 



An annual closely resembling and usually confused with the 

 wild mustard (Brassica Sinapistrum, Boiss.), but is smooth 

 throughout and is rarely so common or troublesome as the latter 

 species, though occasionally found in grain fields and waste places. 

 Its smooth, bluish stem and upper leaves, sessile and clasping, 

 easily distinguish it from the two below. 



20. * BRASSICA NIGRA, Koch. Black Mustard. 



An occasional escape from gardens, but nowhere troublesome 

 or difficult to restrain. Rarely persistent. 



