DESCRIPTIONS OF SOME COMMON WEEDS 1 93 



twelve-celled. Fruit various. Troublesome weeds. In- 

 jurious in wool. 



Ground Bur-nut or Caltrop (Tribulus terrestris). Com- 

 mon in places along the sea coast, Nebraska and Iowa, 

 Plant with pinnately compound leaves, small axillary yel- 

 low flowers, and burlike fruit. 



Spurge Family (Euphorbiaceae). Herbs, shrubs or 

 trees, usually with a milky, acrid juice, opposite, alternate 

 or verticillate leaves and mon- 

 oecious or dioecious flowers, 

 much reduced, subtended by 

 bracts resembling a calyx or 

 corolla; ovary usually three- 

 celled ; ovules one to two in 

 each cell, pendulous; stigmas 

 as many or twice as many as 

 the cells; styles generally 

 three; fruit a capsule, separat- 

 ing elastically into a two- 

 valved capsule ; fleshy or oily Fig. 123. Caltrop (Tribulus 

 endosperm; seeds with flat terrestri *)- 

 cotyledons. 



Bull Nettle or Tread-softly (Jatropha stimulosa, 

 Michx.). A stinging perennial herb, six inches to two 

 feet high ; leaves roundish, heart-shaped, three to five- 

 lobed on long petioles, divisions entire or cut; flowers 

 monoecious or dioecious, fragrant in a terminal, forking 

 cyme; calyx, corolla-like, white, often salver-shaped in 

 staminate flower, five-parted in pistillate flower; stamens 

 monadelphons at base ; capsule, a three-celled, three- 

 seeded pod, with a caruncle. Dry soil from Virginia to 

 Texas. 



Hogwort (Croton capitatus, Michx.). A soft, densely 

 woolly annual, somewhat glandular, growing from one to 

 two feet high ; occasionally branched ; entire, lanceolate- 

 oblong leaves with long petioles ; flowers of two kinds, 



