4 BULLETIN" 233, U. S. DEPARTMENT OF AGRICULTURE. 



rocks and on the small islands in the bed of the wash wherever there 

 is sufficient moisture and enough protection from the force of the 

 current in flood seasons. (PI. I, fig. 1.) Many of the small washes 

 down near the base of the mountains, not large enough to deserve 

 the title of canyon, support great numbers of the plants. Following 

 down from such situations the plant is found in the arroyos extend- 

 ing out through the mesa and often at quite a distance from the 

 mountain range proper. (PL I, fig. 2.) The economic significance of 

 this lower distribution will be discussed later in the present paper. 

 In the ranges where the weevils have been found their distribution is 

 very nearly as wide as that of the plant. 



The Thurberia plant is a large, woody perennial and frequently 

 reaches a height of over 10 feet, though the plants ordinarily met are 

 from 4 to 6 feet tall. (PL II.) The stem is very tough after the 

 first year's growth and supports an abundance of wide-spreading 

 branches. The close relationship of the plant to cotton is quite 

 apparent, and particularly so during the flowering period. A great 

 number of buds (corresponding to the "square" of cotton) are pro- 

 duced. After blooming the square forms a small boll not unlike that 

 of cultivated cotton, varying from one-half to three-fourths of an 

 inch in length when fully developed. When these ripen and dry they 

 open and expose the three to five cells, each containing a double row 

 of angular, blackish seeds covered with a fine pubescence. More or 

 less fiber resembling that of cotton is present in nearly every boll. 

 It is in this boll that the weevil breeds. 



The flowering season of Thurberia depends upon the location, 

 moisture, altitude, and various other conditions. In practically 

 all localities in the mountains around Tucson the leaves appear in 

 April or May. In the lower, moist spots the plants bear fruit buds 

 almost immediately and many fruit prolifically at this time. After 

 two or three weeks of this flowering the buds cease to appear and 

 there is a, quiescent period during which the fruit ripens. Then 

 another crop of buds appears and the same course is repeated. In 

 this manner as many as four crops have been noted on a few plants 

 during the season of 1914 and many bore three. This condition was 

 found only at altitudes below 3,000 feet. Many plants midway up 

 the mountains bore a partial crop in July and then had a heavy one 

 in August and September, while others at much the same altitude 

 had only the latter crop. Throughout the entire upper distribution 

 (above 4,500 feet) the plants grew luxuriantly all summer, but not 

 a single fruiting bud was produced until August. Then an enor- 

 mous crop appeared, and flowering continued until the latter part of 

 September. This flowering evidently varies in the same situations in 

 the different seasons according to the amount of rainfall. 



