THE FLORA OF THE PRAIRIES. 581 
plant (S. perfoliatum), from the large opposite leaves of the 
stem being connate at their bases, forming a considerable 
cup-like cavity, capable of containing water, is common in 
the moist ravines. Other remarkable forms are the Indian 
plantain (Cacalia tuberosa), conspicuous for its thick, 
smooth, plantain-like leaves, deep-green on both sides and 
strongly ribbed; and the yucca-leaved rattlesnake master, 
or button snakeroot (Eryngium yuccefolium), with its linear 
grass-like, bristly fringed leaves, and its bracted flowers, 
closely sessile in dense heads, —an umbelliferous plant, but 
wholly unlike the generality of the species of the Umbellif- 
er&, both in its foliage and in the form of its inflorescence. 
The prairie clovers, or turban flowers (Pentalostemon) , are 
among the most interesting of the leguminose species, and 
among the most characteristic. Their oblong or cylindrical 
heads . of white or purple flowers are evidently: suggestive of 
the latter name. Each head continues in flower for many 
days. At first the flowers form a band at the base of the 
head, which, gradually moving upward, later occupies the 
middle of the head, and finally its summit, recalling the 
Oriental head-dress, in allusion to which these plants here 
received one of their common names. 
The habits of some of the sunflowers, but especially those 
of the Helianthus rigidus, present one feature of interest. 
The H. rigidus is one of the earliest flowering species 
and one of the most abundant ones, it being in some locali- 
ties one of the most conspicuous and characteristic plants. 
By the middle of August it has attained nearly its full 
height, which commonly ranges from two and a half to four 
fees the terminal heads of ae earlier specimens have already 
begun to unfold their yellow rays, and those of the rest are 
nodding on their flexible stalks. It isa popular belief that 
the sunflower always turns its flowers towards the sun, but 
in reality so numerous are the exceptions to this rule in our 
garden sunflowers and in our common wild species of the 
East, that few observing people regard it doubtless as other- 
