Description of the Guayule. 



47 



composed of three morphological elements, fused above, but more or less 

 loosely connected below; a rare occurrence, analogous to the condition 

 of some stamens. The middle element 

 is the narrowest, and is the bract proper 

 of the pistillate flower. This, to be seen, 

 must be dissected out. 



Another peculiar feature then be- 

 comes apparent, namely, that the two 

 disk flowers can not be separated from 

 the achene without pulling away two 

 narrow strips of tissue from its margins. 

 (Fron et Francois, 1901.) The whole 

 arrangement would appeal to the tele- 

 ologist as an excellent adaptation for 

 dissemination by the wind or by water, 

 since the thin, light, and air-imprison- 

 ing tissue may serve as wings or floats 

 according to circumstances. The achene 

 itself is crowned by the persistent but 

 shriveled corolla, and at either side of 

 this and against its ventral (upper or 

 inner) aspect are three short awns, 1 one 

 in each position, The achene proper 

 is ovate, with an acute base. It is par- 

 tially clothed with short appressed hairs , 

 but for which the pericarp would be 

 black or dark gray. The achene meas- 

 ures 2.5 mm. in length by 1.8 in breadth 

 when of normal size, exclusive of the 

 awns. 



The "seed" of the two other spe- 

 cies, mariola (P. incanum) and P. hys- 

 terophorus 2 (an annual) , which grows 

 with or near the guayule, may be 

 distinguished by attention to the char- 

 acter of the lateral awns, which may 

 readily be seen with a lens by viewing 

 them as they project beyond the bract. 

 In the guayule the awns are brown, 

 with papery, denticulate margins. In 

 the mariola these are slender, appearing 

 denticulate or quite without membra- 

 nous margins, tapering and distinctly 

 reflexly curved, and are usually darker in color, being black toward the 



1 Taxonomic works usually indicate that there are only 2 awns, but this is 

 an error. There are 3 awns in Parthenium argentatum and P. incanum; 2 in the 

 herbaceous P. lyratum and P. hysterophonis. Engler and Prantl describe the genus 

 as having 2 to 3 awns, but do not indicate further details. 



2 This plant grows in great profusion in the summer months in the alluvial 

 plains upon which the guayule lands border. 



Fig. 8. 



I, a fully germinated seedling of 

 guayule, before induration, X 8 ; B, cotyle- 

 dons and first two foliage leaves ; C, trans- 

 verse section through achene of a ray flower 

 and its two attached disk flowers. 



