DEPARTMENT OE BOTANICAL RESEARCH. 55 



The Hibernation of a Desert Beetle (Leptinotarsa decemlineata), by 

 J. K. Breitenbecker. 



The extensive cultures of Leptinotarsa, which have been carried on chiefly 

 for the purpose of obtaining results in connection with Prof, W. L. Tower's 

 researches upon the influence of environment on heredity, have furnished 

 opportunities for an experimental study of the habits of these beetles in the 

 desert climate of Tucson, which runs a course generally parallel to that of 

 the original habitat in southern Mexico. Two generations are produced annu- 

 ally, and the later one each year usually goes down into the soil to a depth 

 of a few centimeters to a point where the optimum water and air content 

 is found and remains dormant until awakened by certain climatic combina- 

 tions. The hibernating period may vary from a few months to several years. 

 Experimental arrangements show that either generation may be induced to 

 hibernate, and also that hibernation may be eliminated for an indefinite num- 

 ber of generations by hybridization and controlled climatic conditions. 



The fundamental activities of this beetle, as well as those of many desert 

 organisms, are directly conditioned by its water-content or water-balance. 

 The water-content of the beetle is determined by the evaporating capacity of 

 the air, the leaf-moisture content of its food-plants, soil-moisture, and tem- 

 perature. Variation in any of these factors may influence not only the hiber- 

 nation, but other habits and reactions. 



Vital Statistics of Desert Plants, by Dr. Forrest Shreve. 



Work has continued on the vital statistics of the giant cactus (Carnegiea) , 

 palo verde (Parkinsonia) , and ocotillo (Fouquieria). Detailed weekly ob- 

 servation of a small area has been made, resulting in an exact record of the 

 germinations and deaths of the above species, together with which has been 

 secured a record of the conditions of atmospheric and soil moisture, upon 

 which the death-rate of seedlings depends. The continuation of this work 

 has emphasized the differences of behavior in establishment that character- 

 ize the different types of desert succulents and sclerophylls. It also empha- 

 sizes the extreme slowness with which even the most typical desert species 

 are able to establish new individuals. Observations will be continued on the 

 same area, henceforth at longer intervals, in order to observe the influence 

 of good and poor seed crops on germination-rate and the eft'ect of the annual 

 variations in amount and incidence of seasonal rainfall on the death-rate of 

 individuals of all ages. 



Additional work has been done on natural populations of palo verde in 

 several localities, in which the rate of establishment for the past 300 years 

 has been determined, by converting the trunk-diameter measurements for 

 the whole population into ages, known through averaged counts of annual 

 rings. While the results for the seventeenth and eighteenth centuries are 

 subject to errors that will necessitate much additional work, the curves for 

 the nineteenth century indicate a decrease in the establishment rate. This is 



