A TRINITY OF COLOR. Ill 



abundant in isolated clumps or small assemblies 

 in the rich alluvial soils along the streams of 

 the Middle- Western States. It furnishes the 

 yellow, the ironweed the purple, and the ever- 

 lasting the creamy white of a trinity of color 

 which enlivens, in late August, the lower por- 

 tions of this old woodland pasture. 



Here and there a tall thistle 29 adds a dash of 

 rose color, blooming, as it does, long after its 

 more common cousin, the field thistle, has rip- 

 ened its achenes. One clump of these thistles 

 which I measured was nine feet in height, over- 

 topping all the ironweeds and even the tallest 

 of the actinomeris. Here and there on the stems 

 were numerous brown plant lice, all arranged in 

 rows, their beaks deeply inserted in the grooves, 

 the head end always toward the ground or base 

 of the plant. The stem must yield a sweetish 

 sap agreeable to the aphids. The involucral 

 glands of this and allied forms also exude a 

 sticky substance which is very attractive to 

 many an insect, and which often serves to en- 

 trap and hold them until they perish. 30 As yet, 



a9 Carduus altissimus L. 



"See "Cnicus discolor as an Insect Trap." In Canadian 

 Entomologist, 1892, 310. 



