18 BULLETIN 193 



their development, can be seen by a comparison of the reproduction in 

 deserted road-beds with that of adjacent areas. These wood-roads 

 receive the full sunlight for a few hours at least on each bright day. 

 Acer seedlings which cover the roadway are as thick as if grown in 

 a seed-bed, whereas very few are found in the woods three rods away 

 where the light was much weaker and root competition with the old 

 stand of trees was more intense. (Plate III). 



The data presented emphasize the fact that in the natural woods 

 variations may occur in the amount of light available for seedlings, 

 that in other words the intensity of the forest shade is an extremely 

 variable factor. (Plate V). 



3. BURLINGTON 



In order to determine the relation of crown cover to the surface 

 of the forest, a series of studies was started in definite areas. These 

 areas were 100x100 feet and were subdivided into 100 squares, each 

 10x10 feet, the boundaries being marked with common wrapping cord. 

 Then a map of the area was made, locating the size and kind of each 

 individual tree, after which the crown was projected upon the ground 

 and mapped. In some instances shrubs and herbaceous forms also 

 were shown". 



These maps and the data previously given show that there is 

 considerable variation in the amount of light reaching the surface 

 under a forest. The attempt was made now to determine the total 

 light that would fall on a group of seedlings during the day, but in 

 view of the lack of satisfactory self-recording instruments this was 

 found to be a very difficult problem. The most satisfactory way 

 seemed to be to determine as accurately as possible by the use of a 

 camera how much light fell on a given point, a method which has been 

 suggested by Frederick (6), but has not been used to any great extent. 

 With the camera located at one and the same point, eight 5x7 plate 

 exposures were made in the college woods on August 3, 1912, beginning 

 at 2 P. M. The camera was pointed successively due east, southeast, 

 south, southwest, west, upward with an eastern angle, directly upward 

 and, finally, upward with a western angle. The first five exposures 

 were meant in a way to follow the course of the sun across the sky. 

 Velox prints were made and the light patches removed, as nearly as 

 this was possible. In some instances it was necessary to estimate the 

 amount to be cut out because of the fine branches and leaves. 



