149] FLORA OF COLUMBIA AND VICINITY 7 



Perche creek is met. Its banks are mainly low and swampy, 

 its cliffs are either low ledges, or wanting altogether. 



4. SOIL. 



The usual soil is a fine silt loam, sticky when wet, but soon 

 drying under the influence of the wind. The alluvial flats are 

 composed of a dark soil, often enriched by humus. Along the 

 streams sandy, gravelly, and pebbly flats are not uncommon. 

 In the swales and about old ponds a black muck is found. The 

 soil of the ravines and hill-slopes is composed of limestone de- 

 tritus and plant-remains. It is rich, but is eroded easily, and 

 where the slopes are not left in forest, there soon remains little 

 but barren rock. A few hills have a peculiar red clay soil, which 

 is manifestly sterile, and supports, wherever it occurs, a xero- 

 phytic vegetation. Finally there are the ledges and rocks, bear- 

 ing ferns and cliff-plants in their crevices, and lichens and other 

 lowly plants on their naked surfaces. It is to be added that the 

 loess occurs to the southward and westward, but I know little of 

 its edaphic possibilities. 



5. CLIMATE. 



The climate of Missouri is essentially continental. From 

 its location it receives the warm winds from the Gulf of Mexico 

 and the cold blasts from the plains of the northwest. The pre- 

 vailing winds are southerly, and to this fact is due the high 

 annual mean temperature, 54.6° F. The storm winds are apt, 

 however, to be westerly or northerly. 



In the following tables are given the mean, the maximum, 

 and the minimum temperatures, of all the months for the nine 

 years during which investigations have been going on, or mater- 



