60 Guayule. 



the period was at an end. This does not mean, however, that fresh flower- 

 buds were not available and ready to develop, but that the water-supply 

 was insufficient to support the heavy foliage and to enable the full devel- 

 opment of the flowers as well. 



The end of the flowering season is shown as much by the abortion of 

 the immature capitula as by any other behavior. This is but the extreme 

 expression of a very general phenomenon, that of the unequal development 

 of the inflorescence in adjoining situations. " When water is abundant 

 the inflorescence is widely spreading, the result of the development of 

 the pedicels (fig. 10), while where the water-supply is meager, but not 

 insufficient for the development of the flowers, the pedicels may remain 

 very short and thus produce a crowded mass of capitula. This condition 

 is usually met with in the field (plate 2) , and between this and complete 

 abortion of the flowers every degree of failure to flower is seen, the result 

 of reduced water-supply. 



While the grand flowering-period falls normally in the summer, the 

 exigencies of rainfall may so modify the rhythm of the plant that it will 

 occur in, possibly, any month of the year. Under irrigation flowering 

 starts in March, 1 and there is sustained a profusion of flowers through 

 April (plate 14, fig. A) and May. It then dwindles, a second period of 

 low maximum occurring in August, to be continued irregularly and with 

 less perfectly developed flowers into November. In the field abundant 

 flowers were observed in October in Durango (Hacienda de los Sombre- 

 retillos) and in Sierra Ramirez, Zacatecas. Up to this time of the same 

 year (1907) no flowers had been produced in the Sierra Mojada on the 

 Hacienda Santa Inez, in Durango, where the guayule plants, forming an 

 almost pure culture, were in a shriveled condition for lack of water. 



Under favorable conditions the development of the inflorescence takes 

 about two weeks. The flowers emit a delightful fragrance which attracts 

 many small insects. Among these visitors mosquitoes were observed, 

 extracting the nectar from the ray-flowers. 



THE PRODUCTION OF SEED. 



Though the maximum number of seeds which may be produced by 

 each capitulum is only 5, the total number yielded by a moderate-sized 

 plant may amount to many thousands. The percentage of viable seed, 

 however, runs small. In a field-plant with well-developed heads less than 

 5 per cent of well-filled achenes were found. In other plants as high as 

 2 5 per cent were found filled. In irrigated plants the percentage rises con- 

 siderably higher, namely, to about 35 per cent. When the achenes are 

 fully ripe the bracts become brown in color and fall away from the pedi- 

 cels quite easily. The collection of seed (Chapte^ IX), which must be 

 done by hand if at all, should begin to give the best results at the close of 

 the first period of flowering. Properly done, the flowers are stripped from 

 the peduncle, which need not be removed from the plant. The nature of 

 the "seed" has already been discussed. 



1 In 1909 flowering did not begin in these plants before the middle of April. 

 Inquiry developed that they had not been irrigated freely, if at all, though of 

 course the soil was much better supplied with moisture than that of the field. 



