FOES IN THE HAYFIELD. 99 



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 toothwort. 

 If so, however, they must acquire 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, 

 flat, 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 

 itch for seeing their own names as authorities at the end 

 of a new species. When there is much variation some 

 forms are sure to possess small points of advantage ; 

 and it is these small points that natural selection soon 

 fixes into permanent characteristics of new races. 



