Description of the Guayule. 59 



gated internodes. Those which are still crowded together in the terminal 

 bud-cluster remain and form the basal leaves of the subsequent season's 

 growth. These leaves are the last to be developed, that is, at the close of 

 the growing-season. Since the length of the season is determined chiefly 

 by the decrease of soil-water, the shape of these last-formed leaves seems 

 to be conditioned by this circumstance. This is evidenced by the fact 

 that irrigated plants, to which water is available, continue to form lobed 

 leaves (plate 21), and even those which compose the terminal bud are, in 

 some plants, as deeply lobed as the rest. 



The winter leaves, as we may call those which persist in the terminal 

 bud, are from i to 3 cm. long by 3 to 7 mm. broad, elongate-ovate, taper- 

 ing into the petiole, entire, or with one or two very much reduced teeth, 

 acute. The summer leaves are 6 to 7 cm. long by 2 to 2.5 broad when full- 

 sized, and are deeply lobed midway the length of the blade. A large 

 amount of variation is met with in these leaves, however, the form depart- 

 ing from the proportion given to a long, slender, merely toothed leaf, 7 by 

 0.7 cm. The summer leaves persist, in field plants, till December or later, 

 at which time they begin to fall. By the middle of February all the leaves 

 excepting the terminal bud-leaves have fallen, leaving the gray twigs bare, 

 each surmounted by its leaf-cluster (plate 14, fig. B). Leaf-fall appears 

 to be a function of drought rather than temperature. Long before falling 

 the leaves show marked shriveling and curling, and fall away as much by 

 drying off as by the action of an absciss layer (see Chapter V) , which is 

 imperfectly formed. In irrigated plants leaf- fall is much less prompt, 

 proceeding from the base of the previous season's growth upward, the pro- 

 cess not being completed much before the following April. 



THE INFLORESCENCE AND THE FLOWERING-PERIOD. 



The growth-period of guayule is indeterminate and is largely a re- 

 sponse to moisture conditions, within certain relatively wide limits (Chap- 

 ter IV). Similarly, the formation of flower-buds occurs as a function of 

 this growth and is not related to temperature or other seasonal conditions. 

 Thus, if the growth is small in amount only that flower-bud which hap- 

 pens to be ready to expand will be developed. If the amount is great a 

 second or even third series of flower-buds may be developed and come into 

 fruition, though it is seldom that more than two series mature in one year. 

 When the summer rains commence the resting buds, with their frequently 

 inclosed and partially developed flower-buds, soon begin to grow, and 

 forthwith the first series of flowers is developed. 



According to my data for 1 908 there was practically no growth at all 

 till somewhat later than May 22. By June 9, in more favorable situations, 

 as in arroyo beds, plants were found in full flower, and by about the mid- 

 dle of the month flowering was well started on the ridges of the foot-slopes 

 and in the hills. In certain unfavorable localities, e.g., on low ridges in 

 the plains west of Cedros, the peduncles had attained, by July 22, only 

 half their normal growth. The flowering of the hill plants continued for 

 a month, seed ripening and new flowers coming on, when, by the middle 

 of August, the vigorous flowering-period was entirely closed. By Sep- 

 tember 9, up to which time there was more or less spasmodic flowering, 



