CHAPTER III. 



DESCRIPTION OF THE GUAYULE, 



Parthenium argentatum Gray. 



SEED. 

 The word seed is here applied in a loose sense, inasmuch as the body 

 to which the term is applied is, correctly speaking, an achene, a one- 

 seeded fruit in which the pericarp remains indehiscent and dry. What 

 passes as "seed" in guayule is a mixture of achenes, sterile flowers, 

 involucral scales, and pedicels, and, inasmuch as the opportunities for 

 sophistication are nearly always at hand, and for the reason that the 

 peon employed for the gathering of seed will not always be diligent in 

 distinguishing between guayule and mariola "seed," the present chapter 

 may appropriately begin with a description of the flower. 



In the genus Parthenium, as in all the Compositse, the order to which 

 it belongs, the flowers are arranged in heads or capitula (fig. 10). In the 



guayule these are about 5 mm. in 

 diameter, and contain two kinds 

 of flowers, commonly known as 

 ray and disk flowers. The rays 

 are normally five in number, and 

 are readily recognized during 

 flowering by the open corollas, 

 which project radially beyond 

 the margin of the capitulum. 

 These only produce seed, each a 

 single one, if fertile. 1 The disk 

 flowers produce pollen but are 

 incapable of setting seed, al- 

 though the pistil is present and 

 serves after the fashion of a pis- 

 ton to eject the pollen, as commonly occurs in the Compositae. When the 

 fruit is ripe and the period of flowering is quite past, the capitulum 

 becomes dismembered in a somewhat unusual fashion. Each ray-flower, 

 the two adjacent disk flowers and their subtending involucral bracts, 

 become attached to each other by concrescence, and fall away as a whole 

 (fig. 7). The remainder, i.e., all but ten of the disk flowers, also remain 

 attached to each other and fall away as a shriveled, conical mass. There 

 remain behind five involucral bracts persistently attached to the recep- 

 tacle which supported the whole. In collecting "seed" all of these are 

 taken, so that it will be seen that the bulk of the material is chaff. 



Considering the fertile flower and its accompaniments, we observe 

 that the achene is hidden between the adjoined pair of disk flowers and 

 its own bract. This bract, which is quite broad and concavo-convex, is 



Fig. 7. Ray-flower with attached disk flowers and 

 the subtending bracts. Parthenium incannm. 



46 



1 Polyembryony occasionally occurs. 



