MICHIGAN ACADEMY OF SCIENCE. 
201 
LIGHT AS A FACTOR INDUCING 
PLANT SUCCESSION. 
FRANK C. GATES. 
Everyone lias noticed that in the dense shade of some trees no blue- 
grass will grow. That the most potent factor involved is light is shown 
Grass •' 
Ohiokweed 
Moss 
April 
1910, 
Sept. 
1910, 
/ Diagram showing the successiv relationships of the 
vegetation under a "basswood tree during the season 
of 1910. 
by the following observations made in Graceland Cemetery, Chicago, 
from 1904 to 1910. If lack of sufficient light is the cause for the absence 
of bluegrass, then readmittance of light — other things being equal — 
ought to be followed by the reappearance of bluegrass. How short may 
be the time involved is shown in this instance under observation. 
In 1904 the ground around a large, basswood tree ( Tilia amcricana) 
was sodded clear up to the trunk. The low widely spreading limbs were, 
however, left untrimmed. They shaded the ground very densely for a 
radius of about three meters. Although the bluegrass was abundantly 
furnished with every necessity except light, as time went on, the blue- 
grass began to die out around the trunk. Moss soon developed in the 
area left bare of bluegrass. At the beginning of the season of 1910 the 
moss occupied a ring about 1.5 meters in width beginning where the 
bluegrass left off and extending to one-half to one-quarter of a meter of 
the tree trunk. There were a few other plants growing in the moss of 
