212 BOTANICAL GAZETTE [MARCH 
consideration are able to live together largely because the main 
parts of their absorbing systems are placed at different levels in 
the soil. For example, Circaea lutetiana has its rhizomes only 
about one inch beneath the surface of the soil; the rhizomes of 
Asarum canadense, Sanguinaria canadensis, and Thalictrum dioicum 
are about two inches deep; those of Podophyllum peltatum and 
Sanicula gregaria average about two and one-half inches deep; 
the bulbs of Allium canadense are placed about three inches, and 
the corms of Arisaema triphyllum about five inches below the surface 
of the soil. The rhizomes of Polygonatum commutatum are produced 
about three inches down, and are later pulled down by root con- 
tractions to a depth of five or six inches. Along with these, of 
course, are the trees and shrubs which have absorbing organs at 
all depths to a distance of several feet. Still another factor which 
tends to make it possible for large numbers of species to live 
together in a forest community is the fact that different species 
carry on their more important activities at different times of the 
year, and so do not interfere with each other as much as they 
otherwise would. It is this that makes it possible to distinguish 
-prevernal, vernal, aestival, serotinal, and autumnal seasons, each 
characterized by the prominence of different groups of species. 
It is not necessary, however, to carry the discussion further 
along this line. It is recognized that there is nothing new in the 
preceding discussion except the point of view. In other words, 
the kinds of interrelations here pointed out are well known to most 
botanists, and for that reason it was considered unnecessary to go 
into much detail; but these interrelations have not usually been 
considered as cases of symbiosis. The redson for dwelling upon 
them here, therefore, has been to emphasize the fact that they are 
instances of the living together of dissimilar organisms, and so 
properly belong in a discussion of symbiosis. This proper point 
of view is preparation for further discussion of the other types of 
symbiosis, some of which are not so well known. 
UNIVERSITY oF ILLINOIS 
Urpana, Int. 
5 SHerFF, E. E., Vegetation of Skokie Marsh. Ill. Sta. Lab. Nat. Hist. Bull. 
92575-6014. 1913. 
