CORRELATION OF VEGETATION AND CLIMATE. 105 
Among the palustrine plants which occur along streams at 7,000 to 
8,000 feet are two species of Juncus and two of Carex which also occur 
in Sabino Cafion, under the most favorable conditions of moisture 
supply, at 3,000 to 3,200 feet elevation. The perennial composite 
Tagetes lemmoni grows along the drier arroyos of the Pine Forest down 
to 6,000 feet, and is found in lower Sabino Cafion growing along the 
margin of the stream at 3,200 feet. Other palustrine plants of the 
Forest region are found from time to time at low elevations along the 
largest streams, but no others have been observed to become thoroughly 
established there. 
The well-known cosmopolitanism of many aquatic plants would 
cause us to expect such behavior as is exhibited by Juncus, Carex, and 
Tagetes in the Santa Catalinas. There are several species of Scirpus 
and Eryngium, and at least one woody plant (Cephalanthus occidentalis) 
which range from the Gulf of Mexico across the southwestern boundary 
of the United States to California. The individuals of these species 
are subjected to a wide diversity of atmospheric humidities, but are 
all found under conditions of closely equivalent high soil moisture. 
A greater interest attaches, in the present connection, to the cases 
of low streamside occurrence of plants which grow typically in upland 
situations. Mention has already been made of the trees of Quercus 
arizonica and Quercus oblongifolia which grow along the Sabino Creek 
at 2,800 feet, about 1,200 feet below their lowest occurrence on north 
slopes. Small plants of Quercus hypoleuca have been found growing in 
deep shade in the bed of Sabino Cafion at 3,200 feet, which is 2,700 
feet below the lowest north slope occurrence of this tree. The first- 
named oaks have descended no further than many other upland plants 
have done, but the last-named oak shows the most pronounced de- 
pression of range that has been detected. 
At the mouth of Soldier Cajion, at 3,000 feet, the writer has found 
one or two individuals each of Dasylirion wheeleri, Mimosa biuncifera, 
Erythrina coralloides, and Asclepias linifolia. At an elevation of 4,500 
feet Dasylirion and Asclepias have begun to appear on slopes of south 
exposure, and at 5,000 feet Erythrina and Mimosa have also left the 
arroyos. 
At 4,900 feet Ceanothus fendleri is found in the shade of oaks on the 
flood-plain of Soldier Cafion. It occurs also at 5,300 feet in similar 
situations at the head of Soldier Cafion, and becomes frequent in the 
Upper Encinal at 6,000 feet. Similarly Quercus submollis occurs near 
the constant water at Horse Camp, in Bear Cafion, at 6,100 feet and 
is of increasing frequence along streams up to 7,200 feet. At that 
elevation and up to the uppermost limit of Pine Forest it is common 
on slopes as well as near streams. Robinia neomexicana is found in 
the flood-plain of Soldier Cafion, near a spring, at 5,300 feet, and first 
becomes a frequent upland shrub of the Pine Forest at about 7,500 feet. 
