434 BOTANICAL GAZETTE [MAY 
demands upon the soil; (4) the aerial shoots may have unlike 
growth-forms; or because (5) even where these growth-forms are 
similar, they may vegetate chiefly at different times of the year. 
According as one or more of these conditions control the floristic 
composition of a given community the community may be called 
complementary. 
5. The root depth having been determined by various factors 
for the different species in a community, the specifically different 
root systems then}function in a complementary or a competitive. 
manner as the case may be. But even if the root systems be com- 
plementary, the community may be competitive because of marked 
competition among the aerial parts. Likewise, competitive root 
systems may render competitive a community otherwise comple- 
mentary. 
6. Through the ability of certain species to utilize different 
strata in the soil, the aerial portions of these plants are brought 
into a closer competition. And with closer competition, the chances 
in the past for further adaptation of similar aerial shoots to 
dissimilar growth conditions must have been greatly increased. 
Hence communities, formerly complementary in a purely edaphic 
way, may have been largely instrumental in the evolution of com- 
pletely complementary communities. In so far as they have been 
thus instrumental, the fact deserves great emphasis, especially 
when we consider the far-reaching changes in form and anatomical 
structure necessarily developed as‘a prerequisite to living in a 
completely complementary community. 
LITERATURE CITED 
1. Atwoop, W. W., and GotptHwait, J. W., Physical geography of the 
Evanston-Waukegan region. Ill. State Geol. Surv. Bull. 7. 1 
. Baker, F. C., The ecology of the Skokie Marsh area, with special reference 
to the Mollusca. Bull. Ill. State Lab. Nat. Hist. 8:no. 4. 1910. 
3. CLements, F. E., Research methods in ecology. 1905. 
. Cowres, H.'C., The plant societies of Chicago and vicinity. Geog. 
Soc. Chicago. Bull. no. 2. 1gor. 
FLAHAULT, CH., and Scuréter, C., Phytogeographic nomenclature. 
Intern. Congress Brussels. Circ. 6. pp. 28-+x. 1910. 
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