1922] McDOUGALL—SYMBIOSIS 201 
not necessarily “‘unnatural.’’ The plants in any forest in Illinois at 
the present time have life problems that are just as real, just as com- 
plex, and just as interesting from an ecological point of view as were 
the problems of plants in the primitive forests. We should make 
every effort, of course, to preserve as much of the primitive vegeta- 
tion as possible, but no ecologist whose location is remote from | 
primitive vegetation need feel that there is nothing he can do, for 
wherever plants grow there is ecological work to be done even 
though the land may all be under cultivation. 
_ The work, a part of which is recorded in the present paper, was 
undertaken for the purpose of making a thorough study of sym- 
biosis in all its phases in the University woods. The present paper 
RAINFALL (IN INCHES) AT URBANA; AVERAGE FOR SIXTY YEARS 
Ja Feb. Mar. ‘April May June July Aug. Sept. Oct. : . TOTAL 
B.10 2.40 3.02 3.47 (4.04 4.21 4-80 3.64 «3.60 9.42 2.49 2.24 96. 8H 
TEMPERATURES AT URBANA; AVERAGE FOR FORTY YEARS 
Jan. | Feb. | Mar.| April! May | June | July | Aug. | Sept.| Oct. | Nov.| Dec. |Aver. 
Maximum....... 57| 60] 72 | 83 | 89 | 94 | 98 | 96 | 93 | 84 | 72 | 58 | 80 
Minimum........ — isi Al 42 | 20 1 30 |} :40-1 62 1:51 | 301 27 1 1a 1 2 125 
Mean....... 26 .6)29.2/39.8)53 .0/62.9|71.9/76.4|74.4/67 .2/55.3/41-5/30-4152-4 
deals primarily with social disjunctive symbiosis, and it is the 
hope of the writer to follow it with others treating of the other 
types of symbiosis. 
University woods 
PHYSICAL ENVIRONMENT 
CLIMATE.—Table I gives a summary of weather conditions at 
Urbana, Illinois, during 1919. The data for this table were kindly 
furnished and the table compiled by the Division of Soil Physics 
of the Agriculture Experiment Station of the University of Illinois. 
There were slightly more clear days in 1919 than usual, but on the 
whole the table is typical of the climate of this region. The 
following tabulations of average monthly and annual rainfall at 
Urbana for a period of sixty years, and of average maximum, mini- 
