24 



SULLEIIX 1091, U. S. DEPAETMEXT OE AGPJCULTUEE. {b'^H.^xJ^^^ 



and vary from a minimum length of 20 to a maximum of 37 millimeters, aver- 

 figing about 30. Count of 2 grams of the above Sporobolus material shows 

 that there are 125 .separate cut sections per gram, or a total of approximately 

 6S0,<Xi0 pieces in this one lot of storage, indicating a remarkable activity on 



the part of the individual rat (PI. VIII. Fig. 1). 



The number of lots of storage {'24:) studied in detail, extending 

 as it does over a period of three years with seasons of varying growth 

 conditions, is not sufficient to permit the construction of a curve 

 showing increase and decrease in cjuantity of stored material with 

 growing seasons and intervals between: but the results indicate a 

 very decided increase during the autumn storing season, and con- 

 tinuing large well into the winter, .since some outside material can 

 still be obtained until midwinter. From about February to April a 

 decrease may be noted, followed, if the spring growth of annuals be 

 good, by a slight increase : and we can very nearly predict the gen- 

 eral character of the increases and decreases hj the precipitation and 

 conseciuent growth conditions. 



Table 2. — Quantity of storage per den eorrelated I'-ith time of year and (iroicth 

 eonditions of preeeding season {chiefly from Z'nited States Range Reserve 

 near the Santa Rita Mountains. Ariz.). 



Deu Xo. 



Date. 



191S. 



1 Feb. 7 



2 Mar. 9 



3 .Tulv 2.5 



4 Sept. 20 



5 Sept. 21 



6 Oct. 17 



7 Dec. 20 



1919. 

 Feb. 7 

 Mar. n 

 Apr. 7 

 Apr. 9 

 Mav 7 



Quan- 

 titv. 



117 



2''S 



Preced- 

 ing 

 season. 



Gocd.i 

 Do.i 



Den Xo. 



Date. 



Grams. 





4.127 



Good. 



3.61.5 



Do. 



401 



Poor. 



734 



Do. 



2. .520 



Do. 



2,31.5 



Do. 



1,247 



Do. 



l.fiOO 



Do. 



370 



Do. 



T>r, 1 



May 11 



1, 590 Do. 



14 



1919. 

 Aus. 8 



1.5 



Sept. 4 

 Oct. 17 



If 



17 



Oct. 18 



18 



Oct. 2.5 



19 



Xov. 1 



20 



Dec. 13 



21 



1920. 

 Jan. 31 



99 



1921. 

 Jan. 1 



23. - 



24; 



Xov. 7 

 Xov. 8 



Quan- 

 tity. 



1.51 



313 



.583 



3,410 



3,026 



2.816 



2.3.33 

 1.68.5 

 5, 7.50 



Preced- 

 ing 



Good. 

 Do. 

 Do. 

 Do. 

 Do. 

 Do. 

 Do. 



Do. 



Fair. 



Good. 



Do. 



1 Changing from poor summer season of 1918 to excellent spring growth of 1919. 



= From near the Sandia ilountains, X. ifex.; others from Tnited States Range Reserve, near the 

 ?anta Rita Mountains. Ariz. 



In presenting Table '2. showing quantity of storage per burrow cor- 

 related with the time of year and the character of the preceding 

 growing season, the fact may be emi^hasized that the growing seasons 

 in southern Arizona are two in number — early spring and midsum- 

 mer. The spring season is the less important, the plants consisting 

 chiefly of a variety of small annuals, while the important range 

 grasses make their chief growth and head out almost exclusively in 

 the Julv-Aufifust rainv season. It mav be noted also that the actual 



