A SECOND OHIO WEED MANUAL. 



336 



Fig. 31. Wild Senna. 



through the mutual working- of bacteria 

 which induce the formation of the nodules 

 seen upon the roots, are capable of appro- 

 priating nitrogen from the atmosphere 

 and storing it up in the plant tissues to 

 be used for food or for restoring fertility. 

 Such of them as possess this valuable 

 power should not be too hastily placed 

 among the weeds. There are a few seri- 

 ous pests, however, in this family. 



172 Black Medick, Yellow Trefoil 

 (B) *Medicago lupulina L. A branch 

 of black medick or yellow trefoil, is illus- 

 trated in Fig. 32. This is properly not a 

 weed in any other sense than its frequent 

 occurrence in other seeds. In this it ranks 

 with white clover and is deserving of be- 

 ing known more generally, while scarcely 

 meriting further recommendation. No 

 other single plant has been sent for iden- 

 tification more frequently the past ten 

 years. It is much less valuable for hay 

 than the tall growing clovers, its chief 

 value being for pasture. It may be recog- 

 nized by the small, dense heads (1-4 to 

 3-8 inch long) of little, yellow flowers 

 and the clusters of black seed pods which 

 turn backward upon the stem on ripening. 

 Its strong resemblance to the clovers is 

 noted by all observers. The elongated 

 heads are in contrast to the globular 

 heads of the clovers. 



Seeds commonly yellow like red clover 

 seed, but smaller; frequent as an adul- 

 teration of alfalfa seed. (See seed cuts.) 



173 Sweet Clover, White Melilot (B) 

 *Melilotus alba Lam. The white sweet 

 clover is very common and a branch is 

 illustrated in Fig. 33. There is also 

 another, 



174 Yellow Sweet Clover (B) *Meli lo- 

 tus officinalis L., which occurs more spar- 

 ingly. The white sort is very frequent in 

 clay ground along roadsides. It grows 

 four to six feet in height and appears 

 very rank. 



There may proper 1 .}' be serious ques- 

 tion about rating these plants among the 

 weeds. The former weed law included 

 them, which appears to be a mistake. 

 Sweet clover seems to prefer hard, trodden 

 ground, and except under cultivation does 



* ig. 32. 



Black Medick. 



