33 STUDIES IN THE VEGETATION OP THE STATE 



oMusata occurs only sparsely and infrequently on the ridge, 

 and also on the low prairies. 



Rosa arkansana is a low bush two to five decimeters in 

 height, frequenting high prairies and slopes. At times it 

 tends to become gregario-copious ; at other times its individ- 

 uals are scattered rather evenly over the formation. The rose 

 averages twelve to fifteen individuals to the quadrat, which 

 number may be doubled under more xerophytic conditions, or 

 reduced to one or two plants in meadows. The prairie rose 

 begins anthesis during the late vernal period and continues 

 throughout the estival aspect. Its large pink or white frag- 

 rant blossoms are among the more conspicuous objects of the 

 early summer aspect, especially when slightly raised above 

 the surrounding prairie, as is the case when the plant grows 

 on slopes. The flowers open at 5 :30 a.m.^ lasting for one or 

 two days. One of the most deceptive of the prairie species, 

 so far as numbers are concerned, is Phi/salift virginiana. On 

 a walk over the prairie, even with careful examination, one 

 seldom sees more than half a dozen individuals ; however, the 

 plant is found in almost every quadrat throughout meadow 

 and prairie formation, sparsely, or more rarely as subcopious 

 2. It is needless to say the groundcherry adds nothing to the 

 tone of the aspect. The plants are small, one or two deci- 

 meters high, and perennial by fleshy rootstalks. AlUonia 

 nyctaginea ovata was discovered at only one station, viz., on 

 Great ridge. In duration, it is a perennial. The flowers are 

 nyctanthous, opening at 4 :30 p.m.^ and closing at 9 :00 A.M., 

 and ephemeral, except on cloudy days. If allogamy is not 

 secured through the agency of "night flyers," the much ex- 

 serted filaments and style become reflexed, frequently de- 

 scribing one or two complete circles and bringing anthers and 

 stigmas together. Autogamy may thus obtain. Asclepiaa 

 obtusifolia is a solitary plant occurring only rarely on the 

 higher prairies throughout its distribution. Its many-flow- 

 ered, mostly solitary umbel of greenish-purple blossoms is 

 raised above the surrounding vegetation by means of a long 



