26 The Botanical Survey of Nebraska 



During the mid-summer weeks the maximum humidities were re- 

 corded as a rule between 2 o'clock and 4 o'clock a.m. 



One would be inclined to interpret such records as these to 

 mean that upon frequent occasions during the night combined in- 

 fluences of habitat conditions produce a higher relative humidity 

 in the habitat that is naturally the most xerophilous. As to the 

 cause of this interesting feature of our records we can scarcely 

 guess at present in the absence of extensive data from a careful 

 investigation of that particular point. Possibly the prairie com- 

 munity transpires more moisture at night than the shrub or 

 woodland communities. If that is true then one can readily under- 

 stand why the hygrometer should read higher in the prairie, espe- 

 cially during a still night, than in the other habitats. It may be 

 pointed out in connection with this matter that as a rule there is 

 usually much more dew in evidence in grassland vegetation than 

 in forest or shrub vegetation in our climate. However, knowing 

 full well of the unreliability of the common types of hygrometers 

 especially with the higher humidities, we are not inclined to place 

 too much confidence in the value of these particular data unless 

 perhaps the readings should be checked hourly during the night. 

 The whole matter may simply represent a trick of the instrument. 

 Nevertheless there is need for a careful investigation of the whole 

 problem of the relative water loss from these types of vegetation 

 and the conditions which determine the same during the night. 



STUDIES IN SUBCLIMAX PRAIRIE, SCRUB, AND FOREST NEAR PERU 



Considerable quantitative evidence has already been given by 

 one of us (Weaver, 1919*) to show that the prairies of south- 

 eastern Nebraska, particularly about Nebraska City and Peru, 

 are subclimax in nature. This is indicated in a number of 

 ways. Although the floristic composition in general is very sim- 

 ilar to the prairies at the stations already described, yet a number 

 of herbaceous, half -shrubby and shrubby species which are ele- 

 ments proper to the woodland flora, occur here only or at least 

 occur much more abundantly than in the prairies westward. 

 Moreover, the actually more favorable climatic complex for plant 



*"The Ecological Relations of Roots," Carnegie Inst. Wash. Pub. 286, 1919. 



32 



