THE AMERICAN BOTANIST 



105 



win's idea of the matter seems the more plausible of the two and 

 we may wait for more evidence before accepting Bateson too 

 literally. Upon the theory he propounds, all yellow flowered 

 species should contain in them the determiner for red flowers 

 and all red fruits possess the capability for yellow ones. 



Prairie Plants. — The region in which this magazine is 

 printed is subject to long summer drouths. When, as fre- 

 Cjuently happens, no rain falls for from thirty tO' sixty days or 

 more in the growing season the effect on vegetation can be 

 imagined. Cultivated crops often prove entire or partial fail- 

 ures unless the farmer anticipates the lack of moisture at the 

 beginning of the season and holds the moisture in the soil by 

 proper cultivation. Even in seasons of drouth, however, the 

 wild plants seldom fail to make a crop. The compass plants, 

 the sunflowers, the wild vervains and many others remain 

 fresh and green long after the grasses have become dry enough 

 for prairie fires, but there is a noticeable lack of plants that 

 flower and fruit at the height of the dry season. In these fre- 

 quent drouths, we see one cause of prairies. Plants that require 

 a fairly constant supply of moisture can not endure the con- 

 ditions here and give up the struggle. Seedling" trees, though 

 doubtless often started, sooner or later find a season too dry 

 for them. Thus the prairies are treeless except along the 

 watercourses. The fires that still occasionally sweep across 

 such areas are extremely harmful to all species that do not 

 have some sort of a perennial stem underground. Prairies are 

 like deserts in that the rainfall is unevenly distributed. There 

 are no deserts in which some rain does not fall annually, while 

 some deserts, at certain seasons are as flowery as any meadow. 

 It is the long intervals between rainy seasons that cause the 

 death of all but the most resistant plants. In the prairie region 

 the drouths are of shorter duration but they are still long- 

 enough to eliminate many moisture-loving plants and to pre- 

 vent the growth of trees. 



