124 Guayule. 



THE PEDUNCLE. 



It has been said elsewhere that the method of branching is correlated 

 with the production of the inflorescences, the terminal new branches in 

 twos or threes being produced by the outgrowth of the uppermost axillary 

 buds below the peduncle. There is but little secondary thickening in the 

 peduncle, while, correlated with its slender character, there is a large de- 

 velopment of mechanical tissue (plate 34, fig. 1). In the young condition 

 the chief points of difference between a peduncle and a definitive foliage 

 stem are the absence of medullary canals 1 and the interruption of the 

 hypodermis by the development of chlorenchyma, without, however, the 

 reduction of the collenchymatic character. There are about 6 to 8 of 

 these longitudinal chlorophyll strips, provided with numerous stomata 

 with their axes placed longitudinally, as is usual. The cortex, which is, of 

 course, primary, has usually 6 resin-canals above to 10 below. There are 

 about a dozen bundles, and these, before secondary thickening is con- 

 cluded, produce a few tracheids, though trachea? are equally prominent 

 constituents of the hadrome. A weak interfascicular cambium is formed, 

 but its cells, without losing their cambial character, undergo sclerosis, pre- 

 serving their rectangular transverse section. Stereome strands are formed , 

 as in the stem, just within the pericycle and in the pith, but their relative 

 amount of development is here much greater. It spreads toward the 

 interfascicular cambium, involving the parenchyma-ray cells, sometimes 

 entirely. The stereome within the cambium thus unites to form a complete 

 stereomatic sheath, or perhaps is occasionally interrupted by incomplete 

 sclerosis of parenchyma rays. Outside of the cambium, the sheath is 

 interrupted by the cortical rays, inasmuch as the cells here do not become 

 sclerotic, except a few adjacent to the leptome-stereome. The non-scle- 

 rosis of the interfascicular cortex comports with the view of the chiefly 

 leptomatic origin of the stereome. The small amount of cortical stereome 

 adjacent to the leptome-stereome may readily be recognized both by the 

 color and shape of the cells. 



In addition to the normal stereome, as this may be called, some of the 

 pith-cells, a few of the outer cortical cells, and some also from the collen- 

 chyma become stereomatic. The chief part of this adjunctive stereome is 

 derived from the pith, which contributes a notable amount to the inner 

 surface of the mechanical sheath. In the basal part of the peduncle a 

 periderm occurs, giving rise to a layer of cork about 0.1 mm. thick. No 

 absciss tissue is formed, and the dead peduncle persists for years until 

 disintegration finally overtakes it. As death extends toward the base of 

 the peduncle, the vessels both of the peduncular wood and that of the 

 adjacent stem become plugged, as elsewhere described. It is a matter of 

 interest to note that the structure of the peduncle is very similar to that of 

 the stem in the mariola (Parthenium incanum) , and bears notable resem- 

 blances also to the herbaceous stems of P. hysterophorus and P. lyratum. 



1 I have seen one canal in the pith on one occasion. 



