ASPECT OF THE VEGETATION ABOUT TUCSON. 69 
cut them off near the base and carry them away to their retreats. Hzlaria 
mutica is a true desert grass which finds a place high up on the slopes, 
where it makes patches of color visible for miles. Cassia covesit opens its 
yellow flowers and forms its pods early, while Franseria deltoidea, a low 
shrub, has its bur-like fruits ready to be carried away by any moving 
thing that touches them early in April. The most striking color of this 
period, however, is that of the globose clusters of Encelia farinosa, nearly 
a yard in diameter, which are so numerous and so dense on the slopes as 
to give a golden color that may be caught by the unaided eye for 7 or 8 
miles. One of the wild tobaccos, Nicotiana trigonophylla, grows among 
piles of rocks or on the edge of escarpments, and its creamy yellow flowers 
open early in February. Verbena ciliata forms low clusters, and the 
individuals in any locality show a range of variation of color of flowers from 
deep pink to pure white, while the flowering season is ended only by the 
spring drought. The creosote-bush, Covillea tridentata, begins to open 
flowers and make new leaves in February and continues in flower for 
two or three months. On the mesas and sandy washes the composite 
Batleya multiradiata opens numerous yellow flowers from its clumps of 
stems, that last with their brilliant yellow effects for many days. Low 
and decumbent on the hill-slopes are the crooked branches of a small 
shrub, Calliandra eriophylla, which forms clusters of flowers of a delicate 
pink and soon matures its fruits, while a second species of the genus, 
less inconspicuous, abounds on the lower mesas. 
The greater number of these perennials cast away their leaves with 
the approach of the high temperatures of April and May, and the stem, 
bulbs, or root-stocks go into a quiescent condition from which they do 
not awaken until the following December or January, eight or nine months 
later, the entire period of activity being comprised within a compass 
of a hundred days. Some, however, like Covillea, with varnished leaves, 
and a few other species with heavy protective coatings of cutin or hairs 
on the foliar surfaces retain these organs during a great part of the year, 
and derive some benefit from the activity of the chlorophyl during the 
intense insolation of the summer months. While the soil is supplied 
with water in fair plenty, at least during the early part of this season, 
the humidity of the air ranges between 30 and 4o per cent and only 
plants with protected surfaces may functionate to advantage in it. 
WINTER ANNUALS. 
Of the large number of herbaceous forms which spring from germi- 
nating seeds in the wet winter season and soon pass the whole cycle of 
existence, a few of the more prominent may be mentioned. 
Astragalus nuttallianus, an innocuous relative of the ‘‘loco’’ weed, 
ripens its curved reddish pods early in March and scatters the seeds in the 
gravel, the small stems withering away long before the summer comes. 
