THE SEASONS. 39 



sprinjj: season is largcl}'^ depondcnt upon full rains to start tho vcji^ota- 

 tion, which grows very slowl}' duriiij^- the winter and matures in the 

 sprino-. Of course not all of the sprinjr plants jrerminate in the 

 autumn, l)ut there is a larjje class of ver}^ conspicuous and im])ortant 

 thinj^s which do germinate as early as the latter part of September, 

 make a good growth l)efore the cold weather sets in, grow very slowly 

 durino- the cold weather, and mature in the spring. This cycle is 

 entirely dependent, howeycr, upon the distribution of moisture. If 

 the months of 8eptend)er and October are dry no germination takes 

 place until moisture comes in late winter. If this continues long- 

 enough in the spring a crop matures; but if not, as is usually the case, 

 these plants dr}^ up and there is no more feed produced until the sum- 

 mer rains come again. 



From April to June, although it is yery dry, there is a considerable 

 deyelopment of i)lants which have some special proyision for retainmg 

 or securing a supply of moisture. The deyelopnuMit of these is usually 

 not perceptible until the season of drought. Indeed, it is after the 

 dry hot season })egins that they begin their growth. Attention should 

 be called here to the fact that it is only those plants which have means 

 of supplying themselves with water that grow during the dry season. 

 Those plants protected b}- varnish, or by having power to discard their 

 leaves, etc., use these contrivances to enable them to live, not grow, 

 during the dry season. The case is very ditlerent with the majority 

 of the cacti, which store vast quantities of water in their tissues. 

 They grow w'ithout apparent hindrance through the dry season of 

 early summer. They are of value as food for stock, and would be 

 closely grazed were it not for their oftensive spines. The native 

 gourds, devil's claw, the native night-blooming cereus {Cereus gregfjii), 

 one of the ground plums {Pliysalis sp.), birthwort {Arutolochia 

 hrevipes), and numerous others that might be enumerated, have storage 

 reservoirs in the form of enlarged roots. These plants, however, are 

 of little forage value. The mesquite, on the contrary, is aide to thrive 

 through a long period of drought with no appreciable storage of 

 water, l)ut it is a very deep-rooted plant, and growing to best advan- 

 tage along river courses and arroyos it gets water from the deeper 

 strata there much longer than the shallow-rooted plants, and is there- 

 fore able to grow well into the summer dry season, if not fully through 

 it into the moist summer season without being checked. During the 

 past 3^ear this tree was in full bloom about the middle of May upon 

 the northwestern part of the large inclosure, and it was almost com- 

 pletel}^ defoliated by a lepidopterous larva by the last of the month. 

 On the 2Bth of June it was again in full bloom and had nearly recov- 

 ered from the effects of the defoliation. During the period from 

 April to June there had been 2.9 inches of rain at McCleary's camp, 

 and but 0.^2 inch at Tucson. The rainfall in the mountains at 



