STRUCTURE OP THE FORMATION 59 



mychogamy might insure autogamy. Nevertheless it is to be 

 observed that only a small percentage of ovaries is fertilized. 



Antcnnaria campestris, the one mat-forming species of our 

 prairies, is a frequenter of high and low prairies and mead- 

 ows, though, from a standpoint of numbers, finding its most 

 favorable conditions in the low prairies. The prairie everlast- 

 ing appears with the other prevernal bloomers, being from ten 

 days to two weeks earlier on southern than on northern ex- 

 posures. The plant is stoloniferous, which character ren- 

 ders it highly gregarious; this latter habit, together with its 

 white- woolly apearance, makes it one of the most conspicuous 

 elements of the prevernal aspect. Anthesis in this species, as 

 in other prevernal bloomers, is closely followed by matura- 

 tion. The elongation of the scape is simultaneous with the 

 spreading of the pappus, which causes the achene to become 

 free from the receptacle. The general distribution of the 

 species over the prairie is evidence of the perfect dissemina- 

 tion secured through the agency of the wind. The above spe- 

 cies, though beginning to blossom during the prevernal pe- 

 riod, mostly continue during the early vernal, and frequently 

 appear more prominent during the vernal than the prevernal 

 aspect. This is especially the case with Antennaria, since the 

 mats are more prominent during the period of maturation 

 than during anthesis. 



The other prevernal bloomers need only bare mention. A 

 few bluish-gray cones of Equisetum arvense are found dotted 

 here and there in the meadow formations during the latter 

 half of the prevernal period. Salix liumilis, a xerophilous 

 woody shrub, one to two meters in height, occurs at one sta- 

 tion in the prairie. Its short catkins of dioecious flowers are 

 observed on the first or second day of April; these flowers 

 are frequented by bees and flies which undoubtedly 

 assist in pollen transfer. The swamp willow, Salix fluviatilis, 

 is found in the meadow formation near the creek, especially 

 in those parts flooded during the spring time. It is to be 

 looked uiK)n as an intruder. The swamp willow is about two 



