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 Canon, 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 Canon 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 Canon 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 Canon, at 3,000 feet, the writer has found 

 one or two individuals each of Dasylirion wheeleri, Mimosa biundfera, 

 Erythrina coralloides, and Asclepias linifolia. At an elevation of 4,500 

 feet Dasylirion and Asckpias 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 fendkri is found in the shade of oaks on the 

 flood-plain of Soldier Canon. It occurs also at 5,300 feet in similar 

 situations at the head of Soldier Canon, and becomes frequent in the 

 Upper Encinal at 6,000 feet. Similarly Quercus submollis occurs near 

 the constant water at Horse Camp, in Bear Canon, 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 Canon, near a spring, at 5,300 feet, and first 

 becomes a frequent upland shrub of the Pine Forest at about 7,500 feet. 



