268 COMMON WEEDS 



The Dodders and Broom-rapes above described are 

 wholly parasitic on their host plants. The following 

 plants are only semi-parasites. Although they possess 

 green leaves and are able to assimilate the carbon 

 dioxide of the air, their roots are attached by haustoria 

 or "suckers" to the roots of grasses and other host 

 plants, from which they apparently take water and the 

 mineral food constituents necessary for their nutrition. 



Where they occur on pastures and meadows an 

 application of 4 or 5 cwt. of salt per acre checks their 

 growth. 



SCROPHULARIACE^E 



Yellow Rattle (Rhinanthus Crista-galli L.), also known 

 as Rattles, Rattle-grass, Cock's-comb, or Horse-penny, 

 is an erect-growing annual, 6 to 18 inches high, with 

 narrow serrated leaves placed opposite one another in 

 pairs on the stem, which is quadrangular and branched. 

 The flowers are numerous and arranged in spikes ; the 

 corolla is yellow, with the lobes of the upper lip blue ; 

 the lower lip is shorter than the upper, and three-lobed. 

 After the corolla has fallen the calyx is tipped with red, 

 and resembles a Cock's-comb. The flowers appear in 

 May, June, and July. The seed capsules are roundish, 

 compressed, and two-valved, and the seeds are roundish, 

 compressed, and winged, rattling in the capsule when 

 the plant is shaken hence several common names of 

 the weed. The word Rhinanthus is from the Greek 

 rhinos, the nose, and anthos, a flower, and therefore 

 means the nose flower. 



This weed (Fig. 74) is partially parasitic on the roots 

 of grasses and other plants, and it was shown sixty years 

 ago that it cannot be cultivated entirely by itself. 1 It 

 is frequently very plentiful in damp meadows and pas- 



1 " Experiments by Prof. Henslow," Card. C/iron., 1848. 



