92 ILLINOIS ACADEMY OF SCIENCE 



increasing the stand upon rocky areas appears to have es- 

 caped notice, although it must be of much importance to the 

 species. By it circular areas with a radius of six to ten feet 

 soon become covered with vigorous young upright shoots. 

 The change in direction of growth of the stem axis is strongly 

 marked and seems to be closely connected with the process 

 of rooting although not always dependent upon it. 



In the Saguenay region occasional instances of layering 

 were seen in Picea canadensis, Cooper's observations were 

 confirmed on Abies balsamea but by far the most important 

 from the ecological viewpoint was its abundance in the black 

 spruce. Often large clumps of small trees could be referred 

 to the parentage of a few individuals although with increase 

 in size the connections became increasingly difficult to trace. 

 Frequently groups of six to twenty closely clustered young- 

 trees marked the spot where a tree of an older generation had 

 stood showing much more rapid replacement than could have 

 been effected by seed. 



University of Chicago. 



(1) Cooper, W. S. Reproduction by lavering among coni- 

 fers. Bot. Gaz. 52 : 569-379. 1911. 



(2) Louden. J. C : Arboretum et Fruiticetum Britanni- 

 cum. London, 1844. 



EVAPORATION AND SOIL MOISTURE ON THE 

 PRAIRIES OF ILLINOIS. 



/ - E. M. HARVEY 



I. Introduction. 



The prairie association is quite common in the Chicago 

 region, where it occurs both as small isolated patches and in 

 rather extensive and continuous areas. The association seems 

 to hold here, at least, the position of a very persistent stage 

 in the succession fcjUowing the sedges in the filling up of 

 ponds and lakes. ( 1 ) Although it is to be considered as 

 decidedly different in many ways from the Western prairies, 

 it gives very much the same aspect, this being emphasized by 

 the characteristic coarse prairie herbs such as species of Rud- 

 beckia, Liatris and Amorpha together with Solidago rigida, 

 Ervngium yuccifolium. Silphium laciniatum, S. terebin- 

 thinaceum and others that occur here. AVhatever may be 

 the final history of these prairies as regards succession, it is 

 noteworthy that they are maintained for extended periods 

 against the encroachment of the forests of the region. 



Since the above general probleim, and others are pre- 

 sented by these edaphic prairies, it seems highly desirable that 

 any quantitative measurements of environmental factors be 

 brought forward. 



