42 



THE ECOLOGICAL RELATIONS OF ROOTS. 



in late summer and in exposed situations. As has already been men- 

 tioned, late-maturing species are not at all abundant. No late- 

 maturing grasses are components of the prairie flora. Flowering 

 begins later and growth continues much longer on north hillsides. 



Soil temperatures on the two exposures differ notably. These data 

 are shown in table 12, which gives the soil temperature at 1 to 5 feet 

 on April 18 and August 15, 1914, on a northeast and southwest slope 

 respectively. 



Table 1L — Average daily evaporation in cubic centimeters on a tiortheast 

 and a southivest slope respectively. 



Date. 



SW . slope. 



191.3. 



May 10.. 



May 15. . 



May 26 . . 



June 3. . 



June 10. . 



June 15. . 



June 25 . . 



July 3 . . 



July 8.. 



July 13.. 



July 18. . 



July 25. . 



July 29 . . 



Aug. 4 . . 



Aug. 10.. 



Aug. 

 Aug. 

 Aug. 



16.. 

 20.. 

 25.. 



Aug. 31 



12.0 

 9.8 

 13.1 

 15.2 

 13.0 

 14.2 

 7.8 

 11.0 

 21.0 

 27.2 

 31.0 

 30.8 

 41.5 

 33.0 

 39.5 

 26.5 

 38.0 

 44.3 

 43.8 



NE. slope. 



10.5 



6.5 



10.2 



10.2 



8.6 



7.8 



5.4 



6.7 



13.5 



14.0 



21.8 



20.3 



26.4 



23.8 



24.5 



15.8 



27.2 



30.0 



27.5 



Date. 



1913. 



Sept. 3 . . 



Sept. 7 . . 



Sept. 13 . . 



Sept. 20 . . 



Sept. 23 . . 



1914. 



May 15.. 



May 21 . . 



May 30 . . 



June 7 . . 



June 15 . . 



Jime 22 . . 



June 29 . . 



July 6. . 



July 13 . . 



July 20.. 



July 27 . . 



Aug. 3 . . 



Aug. 10.. 



Aug. 15 . . 



SW. slope. 



33.0 

 32.1 

 33.6 

 46.0 

 21.0 



20.1 

 19.0 

 17.8 

 20.0 

 16.1 

 32.1 

 19.0 

 27.2 

 44.0 

 44.8 

 49.0 

 51.5 

 57.8 

 64.0 



NE. slope. 



21.7 

 21.6 

 23.8 

 20.0 

 17.0 



19.0 

 15.1 

 15.6 

 11.2 

 12.5 

 19.0 

 12.8 

 22.5 

 30.5 

 26.0 

 32.0 

 42.6 

 39.1 

 50.1 



The daily midsummer range at a depth of 3 inches on the northeast 

 and southwest slopes was 12° F. and 26° F. respectively. It is probable 

 that these differences in temperature have considerable effect at least 

 on the rate of root development (Cannon, 1918). 



Summarizing briefly the factors of the habitat in which these 

 studies were carried on, we find a region of moderate winter and low 



