54 Guayule. 



which develops apace, and ultimately becomes an independent plant. The isthmus 

 of tissue between it and the parent plant does not enlarge much in any case, so that 

 it is quite easy, on taking up a bush of mariola, to separate it into several smaller 

 plants by merely breaking off the functionally independent elements. Thus the 

 habits of mariola and guayule in this regard are so different that one plant, the former, 

 remains a single-stemmed shrub of tree-like habit, while the mariola is of the bushy 

 habit. This marked difference, it will be seen, precludes the advisability, though 

 the possibility might remain, of grafting the guayule on the mariola, a suggestion 

 which has been made on the assumption that increased growth might follow in the 

 scion. No economic result would follow, and for this reason: Suppose that we suc- 

 cessfully graft a piece of guayule on a stock of mariola. The scion grows, but at the 

 same time new shoots arise from the base of the stock as described, and their growth 

 is so rapid that in a month or two the guayule shoot is overtopped, and this ends the 

 usefulness of the graft for economic purposes. We might very well make a graft 

 for the purposes of pure science, but economically it would be a failure (Lloyd, 1908c) . 



Recently it has been proposed (Escobar, 19 10), but with admirable 

 reserve, that the dissemination of guayule seed in areas where only ma- 

 riola grows may be attained by grafting guayule upon it. The plan ap- 

 pears impracticable. 



METHOD OF BRANCHING. 



It has been pointed out above that the monopodial growth of the 

 seedling is brought to a close by the development of the first inflores- 

 cence. Following this event, several of the uppermost branches make 

 a more rapid growth. These branches in turn end their growth each by 

 the formation of an inflorescence, when usually the two or three upper- 

 most buds continue to lengthen. Thus is produced a constantly divari- 

 cating system of stems (plate 11, fig. A), which, if uninjured, results in 

 a splendidly symmetrical and closely branched shrub. A very excep- 

 tional plant, approaching the ideal form, is seen in plate 11. Through 

 failure of some branches to develop, irregular forms are often seen. These 

 usually attain a greater height than the symmetrical plants. An unusu- 

 ally tall plant is shown in plate 10, in which the irregularity of growth 

 is illustrated, while in plate 11, fig. B, a form more frequently met, espe- 

 cially in very rich fields, is shown. 



A comparison with the mariola is here pertinent, as there appear 

 to be two types of guayule in respect to the manner of branching, one of 

 which approaches the condition in mariola. The usual manner of exten- 

 sion of the branching system is by the nearly equal growth of two or three 

 branches just below the inflorescence (plate 14, fig. B). As will be seen, the 

 anatomical distinction between stem and peduncle is abrupt, and the dead 

 and, according to age, more or less disintegrated peduncle remains as a 

 spur in the angle between the uppermost branches. Often this may still 

 be seen after the lapse of many years. No absciss layer is formed, 1 and 

 this again gives a suggestion of the recent departure of the shrubby type 

 from the herbaceous ancestor. After flowering, the dead peduncles re- 

 main in evidence above the foliage of the plant and form a conspicuous 

 character. In the mariola, on the other hand, with the same morphologi- 

 cal basis, a different habital form is had. The stem, as in guayule, ends 

 in an inflorescence, is more slender, and is beset with short branches or 



1 This condition is, of course, common to many plants, and is specially preva- 

 lent among the Compositae. 



