304 CARNEGIE INSTITUTION OF WASHINGTON. 



that the plant is necessarily the best measure of optimum conditions 

 for its growth and reproduction. As a consequence of its association 

 with other species in definite communities, it serves as an index to the 

 possibilities of both soil and climatic areas. When the successional 

 position of an indicator has been determined, one can not only predict 

 what plants and communities will follow it naturally, but can also 

 determine what plants will enter in consequence of overgrazing, fire, 

 lumbering, etc. It is the successional significance of a dominant 

 species which makes the use of indicators so indispensable in grazing 

 and in forestry. ^Vhen the presence of an indicator is checked by the 

 number and size of its individuals, a scale of extreme sensibility is 

 obtained, on which it is possible to read accurately the variations of one 

 year and to forecast with certainty those of the next. Moreover, by 

 the correlation of dominants with the physical factors of the environ- 

 ment, and especially the determination of their water, hght, and tem- 

 perature requirements, they may be used as crop indicators, particu- 

 larly in dry-farming operations. Grazing indicators have naturally 

 received the most attention during the present summer, but this has 

 necessarily involved a study of dry-crop indicators as well. The suc- 

 cession research of the preceding four years and the quantitative study 

 of habitats and dominants at the Alpine Laboratory from 1900 to 1912 

 have produced a large amount of material on forest indicators espe- 

 cially; this has been checked byspectrophotometric observations during 

 the present summer, and it is hoped to present the combined results in 

 a manuscript available in December. 



Climatic Cycles. 



The most attractive and promising feature of the summer's work has 

 been the tracing and checking of the course of the present chmatic 

 cycle. The second recorded absolute minimum of no sun-spots occur- 

 red in 1913, and served as the focus of a period of exceptional rainfall in 

 the West. The drought of the present sunmier in the Western and 

 Mountain States suggests the beginning of the dry phase of the cycle. 

 Its effect upon the carrying capacity of the ranges and upon the pro- 

 duction of dry farms has been critical. Whether it be followed by the 

 full period of several dry years or not, it has furnished further confirma- 

 tion of the fact that all grazing and dry-farming must be based upon the 

 recurrence of dry periods ; in both, a scientific system of expansion and 

 contraction must be devised to prevent disaster during dry years. If 

 the next two or three years prove to be dry in harmony with the maxi- 

 mum of the sun-spot cycle, the possibihty of anticipating dry seasons 

 will be greatly enhanced. In the field of forestation much evidence has 

 been obtained to show that planting is successful only during wet 

 phases and that natural reproduction occurs practically only during 

 such phases. It is obvious that no other scientific advance will mean 



