ENVIRONMENTAL AND HISTORICAL FACTORS. 95 
the records for July 14-15, 1906, give an aggregate rainfall of 1.16 inches 
at the Desert Laboratory and 0.49 inch at the Experiment Station, 
while for August 10-11, 1906, the amounts recorded are a trace at the 
Laboratory and 0.88 inch at the Experiment Station. Enough is known 
of the habits of the plants of the Laboratory domain to establish the 
fact that such differences of precipitation profoundly affect development, 
and in critical years may be associated with conspicuous failure on the 
part of many species of annuals to appear in their customary places. 
TABLE 6.—Records of Rainfall at Desert Laboratory and University of Arizona, 
March, 1906, to May, 1907, inclusive. 



















Date. Lab. | Univ. Date. Lab. | Univ. Date. Labs 4 Untv; 
1906. Inches. | Inches. 1906. Inches. | Inches. 1907. Inches. | Inches. 
Mis ratte Os OL 75 MPAs ter Uo tei ec Tat MA BSiO .0O2%) fa 202 
eo | Cee “E3 Ince O-O0Le | O00 Cieiae coats 1% 
Doe Ren. fie Fis datire ey: . 42 ee fo See Ae 
Pe. Oi. 0.03 Por) O47 0.59 5 RA Oe ee O.O1 
ZOnn O.. 23 0.26 TO Oe sO) HLOs2s ES fa LO ex 
ZT et O.0225) 0.045 COM Oar | Orse 16-2) 0.02 }.0.20 
P 8 0Ces engage. ae ; cee cae O.OI Cte) Sater ah: 
mote O- 1-0 .01 |. O-30 ig ii. aera LO Meee eat o.25 
PIANO 34 0.14 BEEN, OOF Ws sts 19.4) O35 Oui! 
May 23) 4) @.0183|"1. One i oe 2OcLNe Lo 0.01 
ty eter 0.02 Brea O.02 1G, OF 2004) On 8F) | 0.20 
tO. O83 50 tr screae: SeEptgn0 yor err fy. Bir ies. Jee O.O1 
Gen peace Pe PA 210) | Osa4 HebuitG. cr 2) 0.035 
LO errr ee 0.04 27 O18 |. 0200 Pore ie O.OI? 
TS, LOMtIVe:, 16 Octo, 01605 141. 2 (ewe SE8e 0.04 
he et eee ee nee NOVA. 1smi.00055 | 0.07 25d 0.08 4. 0.025 
oe. el, aye a aso eee ‘ FW ha cea im! 
1451 GOO WO 440 LOM. OrAUS) | O52 Mag. 95: 210.256 1.0240 
Ih ach 0.27. -|.0,09 2A 2) O219e OnL5 22 el OSLO) On 1G 
TO eee 0.04 SSE DU haste: 218% aad Meds a ec 
Bia) bees, ce O.O1 Decoy 2 io.65a) |:o390 ie tala) Ls) ey teed 
EA eee ‘ie Beles OO tee aT 5 CA ANE 0.015 
2) nt a Velho Mi ees elt DB ly eee es ee i da eae Te 
260150702 1.06 Deir Oper Mata Lt oy perk he ae eee 
ae POROOS | oan AOpen ST 1 Oe 20 este ti Ake ‘be 
i: A pS al AORN Pana 0.03 AS hosed le se ws At 
AT eye ihe 1907. Mayon oto jee 
Aum erie OsrTeo to. 3r SY ioe ie aah Bey et Pho ad cesar 0.06 
les Wee ; Zee O-OF Outs 2Ot| Orton | Ort 
Toa) als 0.26 Che SOLOL= WOe1G 
5% Sie ea 0.62 ide aed 0.08 
1Snow. 
The records of table 6 are also of importance in connection with the 
measurements of the sahuaro, which prove its capacity for the prompt 
absorption and storage of water after even very light rains. ‘There can 
be no doubt that by this means the giant cactus is placed at a distinct 
advantage throughout its range and in its association with more deeply 
rooted plants. 
More definite, as regards the intimate relation existing between dis- 
tribution of precipitation and of vegetation at various points in southern 
Arizona, is a recent paper by Prof. J. J. Thornber to which I am per- 
mitted to refer in advance of its publication elsewhere. A comparison 
