20 BOOKS AND CURRENT LITERATURE 



The influence of man on the distribution of hardwoods is even more 

 noticeable than among the conifers. Most important, the hardwood 

 forests being in the zone of husbandry had to give way rapidly to cul- 

 tivation; furthermore, they suffered severely because of a shortsighted 

 and wasteful management of what was not cleared. There followed 

 also as a consequence an extension downward of the coniferous zone 

 brought about iby the release of conifers from competition with the 

 hardwoods where the two were in mixture. In contrast to the restric- 

 tion of the hardwood forest due to cultivation is the extension and 

 spread of single species over a wide ^rea, the habit of alder in particular 

 in invading newly cut coniferous forests in the sub-alpine zone being a 

 good example. 



As a thorough piece of work Dr. Hager's contribution deserves com- 

 mendation. Considering the area -under investigation, only about 300 

 square miles, his book of over 300 pages seems hardly warranted from 

 an American point of view until one considers the more intensive rela- 

 tionship existing between man and his surroundings in an old country 

 like Switzerland. The work should be of value to the student of 

 ecology as well as the student of scientific forestry. — Emanuel Fritz. 



Spectral Color and Stimulation. — The paper under notice' is 

 a continuation of a series of studies in light response of lower organisms 

 which, although more largely concerned with algae than the lower 

 animals, are unfamiliar to most botanists since the results have been 

 published in zoological periodicals. In the author's previous studies 

 he found that in a field of white light consisting of two beams crossing 

 at right angles, the organisms proceeded towards or away from a p: int 

 situated between the two beams ; the location of this point being depen- 

 dent upon the relative effectiveness of the two beams. The present 

 series of experiments is based upon the assumption that if an organism 

 exposed to light from two sources proceeds towards or away from a 

 point midway between the two, the light received from the two sources 

 is equal in stimulating power no matter how it may differ in quantity 

 or quality. Knowing the wave length of the beams of light producing 

 the field of illumination it is possible to compare the stimulative 

 effect of rays of light of different wave length. 



Although a large number of investigators have studied the effect 

 of different qualities of light upon plants but few have taken up the 



iMast, S. O. The relation between spectral color and stimulation in the 

 lower organisms. Jour. Exp. Zool. 22: 471-528. 1917. 



