466 



PRACTICAL BOTANY 



sun plants and shade plants, or into drought-enduring and 

 moisture-loving plants (Sects. 441-446). We are fortunately 

 as yet but little troubled in this country by one obnoxious 

 group of weeds, the parasitic flowering plants. The clover 



dodder (Fig. 351) is one 

 of the most important of 

 these, causing much trou- 

 ble in fields of clover and of 

 alfalfa. The farmer would 

 often class weeds accord- 

 ing to the kind of crop with 

 which they interfere ; for 

 example, into weeds of pas- 

 tures and those of culti- 

 vated ground, subdividing 

 the latter group into weeds 

 of cornfields, weeds of oat 

 and wheat fields, weeds of 

 clover fields, and others. 



432. Qualifications for suc- 

 cessful weeds. Not many 

 wild plants of any region 

 can become, even in the ter- 

 ritory to which they are 

 native, successful weeds. 

 The trilliums, columbines, 

 pepperroots, fire pinks, wild 

 ginger (Fig. 43), Dutch- 

 man's-breeches, and wild 

 sweet William (Phlox), so 

 familiar among the early 

 wild flowers of the Middle 



West, are there practically unknown in cultivated fields. For 

 various reasons the conditions of life in tilled ground are 

 promptly fatal to them. In order to push its way among com- 

 petitors, to win in the struggle for existence, under natural 



FIG. 351. Clover dodder, parasitic on 

 red clover 



A, habit sketch of part of the parasite and 

 the host ; B, portion of stem of the dodder, 

 showing protuberances from which haus- 

 toria pass into the stem of the host ; C, 

 a single flower of the dodder. B and C 

 considerably magnified. Modified after 

 "Flora Danica " 



