IQO COLL\ CLOUT'S CALENDAR. 



swHinps, and feed only at tlie expense of the rank grass 

 in water-logged patches of meadows. Then come the 

 still more parasitical cow-wheats, very injurious to 

 standing corn, but happily rare in England except on 

 the south-east coast. In Norfolk, purple cow-wheat is 

 a regular pest, one of the worst possible corn-field weeds, 

 and very difficult to eradicate, since it sheds its seeds 

 before the harvest is reaped. This plant shows in an 

 incipient form the common tendency of advanced 

 parasites to lose the greenness of their leaves ; and 

 when once a weed has finally reached that depth of 

 degradation it must feed for ever in future upon the 

 juices of its host, having no chlorophyll of its own with 

 which to assimilate starches for itself from the air. Last 

 of all, yellow-rattle completes the list, and draws more 

 than half its sustenance from the throttled grasses 

 on which it fastens. In time such plants may sink to 

 the absolutely leafless condition of broomrape or tooth- 

 wort. 



If so, however, they must ac(iuire some plan for 

 diffusing their seeds more widely and more certainly, so 

 as to fix themselves from the first on the tissues of some 

 other weed. At present the seeds of rattle are large, 

 Mat, and winged ; and when ripe they clatter about 

 noisily inside the swollen calyx and pod, till a high wind 

 blows them out and away. Children shake the pods to 

 make them rattle, which gives the weed its common 

 English name. The variability that has made the 

 whole family what it is may still be marked with our 

 own eyes : for both rattle and eyebright have so many 

 varieties and transitory forms that they have been split 

 up into numberless separate races by botanists with an 



