76 VICTOR E. SHELFORD. 



(a) Temperature. The above data on the temperature of 

 the surface of the soil may be caken to represent essentially 

 the temperature at the surface as well. There are no records of 

 the temperature at various heights above the ground. Notice- 

 able differences within the height of the trees present, are to be 

 expected particularly in the cottonwood and other early stages 

 where much bare sand is exposed. 



(b) Light. Animals are either positive or negative to the 

 actinic rays of the spectrum (Congdon, '08, Mast, 'n). Con- 

 siderable work has been done by plant ecologists, on the measure- 

 ment of light with photographic papers but its bearing on plant 

 problems is questioned by some because the nonactinic portion 

 of the spectrum is most important in the process of photosynthe- 

 sis. It appears that these measurements are of much greater 

 significance for animals than for plants. Zon and Graves ('n) 

 have brought together the literature and discussed the methods 

 of study (see especially several papers by Wiesner). 



The light in the cottonwood stage is more intense than in any 

 other of the habitats that we are to consider. Tests of the light 

 in the beech woods and in the road adjoining, made with a Wynne 

 exposure meter, show the following differences : 



Time Required to Match 

 Location of Meter. Standard Tint. 



Beech woods darkest shadows 1,200 seconds. 



Beech woods medium shadows 180 



Beech woods brightest spots 10 



Road on the north side of woods 3 



While the above table shows a measurement of the actinic 

 rays only, it indicates that in the beech forest, such rays at least, 

 are diminished in intensity to from 1/3 to 1/400 that of full sun- 

 light. On account of the great amount of reflection from sand, 

 the light in the cottonwood stage is probably double that in the 

 wagon road which is bounded on the south by beech woods and 

 on the north by second growth timber. 



(c} Combinations or Complexes of Factors. As we have already 

 pointed out (Shelford, 'n), the animal environment is a com- 

 bination of moisture, temperature, light pressure, materials for 

 abode and food, all of which factors taken together constitute a 

 complex of interdependences. These various factors are so 



