24 BULLETIX 1091, U. S. DEPARTMENT OE AGRICULTURE. {b^L^kI. 
and vary from a minimum length of 20 to a maximum of 37 millimeters, aver- 
aging abour 30. Count of 2 grams of the above SporouoJus material shows 
that there are 125 separate cut sections per gram, or a total of approximately 
680.000 pieces in this one lot of storage, indicating a remarkable activity on 
the part of the individual rat (PL 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 quantity of stored material with 
growing seasons and intervals between: but the results indicate a 
very decided increase during the autiunn 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 by the precipitation and 
consequent growth conditions. 
Table 2. — Quantity of storage per den correlated icith time of year and groicth 
conditions of preceding season (chiefly from United States Range Reserre 
near the Santa Rita Mountains. Ariz.). 
Per X: 
Date. 
Quan- 
tity. 
Preced- 
ing 
season. 
191S. 
Grams. 
Feb. 7 
4.127 
Good. 
14 
Mar. 9 
3.615 
Do. 
15 
Julv 25 
401 
Poor. 
If 
Sept. 20 
734 
Do. 
Sept. 21 
2.520 
Do. 
1^ 
Oct. 17 
2.315 
Do. 
19 
Dec. 20 
1.247 
Do. 
20 
1919. 
Feb. 7 
1,600 
Do. 
21. 
Mar. 13 
370 
Do. 
Apr. 7 
ISO 
Do.- 
Arr. - 
117 
Gocd. 1 
■» 
Mar 7 
2** 
Do.* 
23 
Mar 11 
1.590 
Do. 
24 
X — 
1919. 
Aug. 8 
Sept. 4 
Oct. 17 
Nov. 1 
Dec. 13 
1920. 
Jan. 31 
1921. 
Jan. 1 
Nov. 7 
Nov. 8 
yuan- 
tity- 
Grams. 
5 
151 
313 
5s3 
3. 410 
3.026 
2.S16 
Preced- 
ing 
=-ascr- 
Good. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
1.173 Do. 
2.333 Fair. 
1. 6S5 Good. 
5, 750 
Do. 
- Changing from poor summer season of 191S to excellent spring growth of 1919. 
= From near the Sandia Mountains. X. Mex.: others from United States Range Reserve, near the 
Santa 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 emphasized 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 July-Auffust rainv season. It mav be noted also that the actual 
