ASPECT OF ‘THE VEGETATION ABOUT TUCSON. 73 
ing appearance of trees. These begin activity early in April, two of the 
earlier ones being O. versicolor and O. spinosior (tasajo), with a puzzling 
range of colorin the flowers. Thus, some individuals will be found which 
have bright crimson or reddish-purple flowers and others with light red; 
others with yellowish-red, yellow, and greenish-yellow, the shade also 
being reflected by the color of the stems, so that the color of the flower 
may be predicted upon seeing the plant from a long distance. In some 
instances two colors appear to be exhibited by a single plant, but a closer 
examination generally shows that what appears to be one plant is in 
reality two, grown together at the base. 
O. fulgida is characterized by the silvery, shiny appearance of the 
sheaths of the spines, and is locally known as ‘‘cholla,” although that 
name properly belongs to a species native to Baja California much far- 
ther south. 
Nearly related to O. fulgida and growing intermingled with it is O. 
mamullata, with more greenish branches, shorter and sparser spines. 
Both of these species have easily detachable branches, and the separ- 
ated portions act as cuttings in propagation. The facility with which 
the joints are cast loose and attach themselves to an animal by the sharp 
spines makes them much to be dreaded, and it is by this means that dis- 
semination is effected ina very efficient manner. The fruits remain 
attached to the branches for one or two years, or even longer, and the 
seeds are exceedingly slow of germination (plate 57). 
Opuntia bigelovit, which is so densely clothed with short silvery spines 
that a pencil-point can not be thrust against the stem without pushing 
several aside, shows anextremely wide range over the deserts of the South- 
west from Death Valley across to the mesas of Arizona and southward 
along the shores of the Gulf, also propagates itself by means of detached 
joints, and an entire colony of these plants may be seen that have come 
from one older central individual. 
Several species of birds make their nests in the branches of the cyl- 
indrical opuntias, where they are secure from hawks and marauding 
animals; and many rodents of the desert drag the detached joints about 
their burrows, making an effectual barricade against the coyote and fox. 
The agaves form their great rosettes of thickened leaves on the slopes 
running up from the greater mesas, and after a period of development 
which varies from a few to many years a central flower-stalk is sent up 
in the foresummer with extraordinary rapidity, growing in length as much 
as a foot a day and quickly forming flowersandseeds. Thiseffort exhausts 
the resources and terminates the life of the individual, and the entire 
cycle of these ‘‘century-plants”’ is directed to this one effort of arriving 
at mature size with an accumulated food-supply that will enable them 
to perfect a cropof fruits and seeds. This habit makes the agaves an 
important source of food for the southwestern Indians, who take the 
