4 THE AMERICAN BOTANIST 



i 



down from Reservoir Canyon a few miles to the east travers- 

 ing on the was a cat-tail swamp. At one point a low dam 

 forms a small lake, in the swampy borders of which the wild 

 ducks nest. Much of this water is used by the Hopi in his 

 irrigation projects and the rest renders fertile the government 

 farm further west. Much of the flood waters from the Black 

 Mesa, fifty miles or more northeast, also runs off through the 

 Wash. Owing to the rocky surface of the country, very little 

 of the rainfall is retained and some hours or days after a storm 

 on the distant heights, a dark and turbid torrent, more like 

 liquid mud than water, pours through the valley, often tear- 

 ing out dams, silting up reservoirs and irrigating ditches, cut- 

 ting new channels, and causing much other damage. 



The highest recorded temperature at Tuba is 108° F. in 

 August and the lowest 13 °F. in December. Much of the 

 year, therefore, is favorable to plant growth, but the lack of 

 water reduces the vegetation to the minimum. As in all the 

 surrounding region, there is a marked difference between the 

 day and night temperatures. Owing to the drv air, cooling 

 after sundown is very rapid and the air ni;iv become decidedly 

 chilly before morning, even in summer. 



The precipitation in the Oasis is insufficient for tlry farm- 

 ing. It is seldom more than six inches a year and a great deal 

 of this falls as snow during the resting season. Under irriga- 

 tion, however, the soil yields good crops of corn, wheat, cot- 

 ton, alfalfa, melons and all the common garden crojjs. The 

 precipitation, moreover, is distinctly seasonal. From the last 

 of March to the middle of July — the season of greatest bloom 

 elsewhere — little, if rmv, rain falls. In 1^)20 there was no 

 precipitation whate\er in .\[)ril. May and June. This uneven 

 rainfall has an important effect on the vegetation. L pon the 

 breaking up of winter, there is sufficient moisture for flower- 

 ing and most of the desert platits burst into bloom. Then en- 



