Periodical Literature. 447 



source of the pollen is known, since among the larger number of 

 plants necessary for such experiments, there may be physiological 

 or ecological races within a species, and such races would respond 

 differently to their environment. The use of homogeneous ma- 

 terial (elementary species or varieties) is an indispensable pre- 

 requisite. 



Another field that is practically virgin to the plant ecologist is 

 exact experimentation in regard to the processes of competition, 

 migration and adjustment in relation to climatic factors. 



C. D. H. 



The Trend of Ecological Philosophy. H. C. Cowles. The American 

 Naturalist. June, 1909. Pp. 350-368. 



The Present Problems of Physiological Plant Ecology. B. E. Livingston. 

 The American Naturalist, June, 1909. Pp. 369-378. 



Vegetation and Altitude. Ch. H. Shaw. The American Naturalist. July, 

 1909. Pp. 425-431. 



Problems of Local Distribution on Arid Regions. V. M. Spaulding. The 

 American Naturalist. August, 1909. Pp. 472-486. 



The Relation of the Climatic Factors to Vegetation. E. N. Transeau. 

 The American Naturalist. August, 1909. Pp. 487-493. 



The results of an extensive series of inves- 



Pruning tigations into the effects of pruning at dif- 



and ferent seasons with different species and 



Increment. locations, on the manner of treating the 



wounds, and increment, made by Zeder- 



bauer at the Austrian Experiment Station, is of interest to us only 



so far as the physiological data are concerned and incidentally 



as far as foresters on this continent are supposed to be general 



"tree-sharps" who should know all about trees, ornamental as 



well as economical. It is, however, possible that in the not very 



distant future, under some conditions, tree pruning may become a 



forest practice. 



As regards the season for pruning, it would appear that spring 

 is the most satisfactory, the operation at other seasons not only 

 delaying the healing process but giving rise to discolorations at 

 the margin of the wound. That the healing process progresses 

 more readily if the cut is made close to the bole is well known. 

 The rapidity of the process depends also upon the species, rapid 

 growers callusing more rapidly, and in the growth conditions 

 generally. 



Among the species investigated Douglas Fir was included. 

 Among other things it was found that just as with deciduous 



