264 



THE PLANT WORLD 



a distinctly deeper tinge to the landscape, those of the palo 

 verde {Parkbisonia microphylla) are very striking by reason 

 of their number, as well as by the persistence of the cotyle- 

 dons which increase in size after germination, serving as foliar 

 organs until the first pair of pinnate leaves are well mature. 

 Summer annuals. Several Euphorbias spread their 

 small dense mats of thin stems and minute leaves on the 

 surface of the ground, and are rich in a latex or. milky juice 

 containing resins, starch, and some caoutchouc, which is 



Pig. 1.— Kallstroemia grandiflora in midsummer. 



reputed by the Indians of various tribes to furnish an anti- 

 dote for the venom of the rattlesnake, a supposition not con- 

 firmed by experimental evidence, however. Another group 

 of species which forms green mats on the surface is comprised 

 within the genus Tribiilus. Some of the plants of a relative, 

 Kallstroemia jrraiidiflora, cover an area of nearly a square 

 yard with a dense mass of green compound leaves offering 

 a background contrasting with the bright yellow and reddish 

 colors of the flowers, which show interesting opening and 

 closing movements. The thin yellowish, almost leafless. 



