BOTANY 



J. J. Thornber, J. G. Brown 



The rainfall for the year ended June 30, 1920, at Tucson. 

 Arizona, was 20.59 inches, or practically double the average annual 

 rainfall for this station. This is the heaviest rainfall that has been 

 recorded for Tucson for a similar twelve-month period during the 

 past 39 years. Of this rainfall, 10.24 inches, or nearly 50 percent, 

 fell during the summer rainy season, July to October inclusive; 

 and 9.18 inches, or 44.7 percent, during the winter rainy season. 

 November to April inclusive. October, December, April, May, and 

 June were the months of lightest precipitation, while for each of 

 the remaining months there was a minimum of one inch of rain, 

 and usually much more than this. The rainfall for July was 26.9 

 percent of the total for the year. 



Naturally, this rainfall resulted in a heavy growth of forage on 

 the ranges during both the summer and fall of 1919 and the winter 

 and spring of 1919-1920. There was an abundance of feed on 

 almost all the ranges, except those badly overgrazed and trampled 

 out, and at the same time a smaller number of stock to graze, since 

 the herds had been much reduced during the two previous years 

 on account of severe droughts. Scarcely more than 70 percent of 

 the feed was eaten during the fall and winter and the plants 

 matured a heavy crop of seed for future growth. Stock, generally, 

 came through the winter in good shape, and the ranges were in 

 better condition than they had been for some years. 



The heavy winter rainfall just noted brought about two con- 

 ditions. The feed on the ranges, which underwent natural curing 

 with the dry weather in October, was badly leached out and 

 weathered before spring. This was largely offset, however, by the 

 excellent spring growth which was ready for grazing by the raiddle 

 of March. The other condition was the heavy growth of poison 

 plants on the ranges, induced by early and continuous winter rain- 

 fall. 



LOSSES OF STOCK FROM POISON PLANTS 



Losses of stock from poison plants were quite general and 

 heavier than for some years past. On many ranges there was a 

 heavy growth of loco and larkspur plants before the grasses and 



