Vegetative Reproduction. 195 



parent plants had been taken from an old stack-ground in Saltillo, at the 

 guayule factory of Martin Brothers, and had started there from seed 

 which had fallen from the stacked guayule. Before being transplanted, 

 they were variously trimmed back, leaving only the lower portions of the 

 main stem and, in some instances, of the lowermost branches. During 

 1907 the new growths attained a length of about 25 cm., making rounded 

 bushes about 15 cm. in diameter. By September 1908 another 25 cm. 

 of growth brought them to a spread of a meter for the largest plants. 



It was then discovered (on the 1 9th of September) that the lowermost 

 new shoots in certain of these plants had struck root, quite after the 

 manner described for the mariola, and it was further observed that this 

 had not occurred in all of the plants, but either in those plants which had 

 been trimmed back so as to leave only a very short basal portion, or in 

 those new shoots which had arisen close to the tap-root (plate 44, fig. A). 

 In several instances the whole of the lowermost branch was buried by 

 chance in the soil, and in others a part, but neither in these nor in some 

 layering experiments by Dr. Kirkwood J was any response observed. The 

 behavior of guayule in this respect is similar to that of certain plants 

 which are subjected to mound-layering. Whether it is possible to compel 

 every plant properly treated to behave in the manner described can not 

 be said, as circumstances prevented a more careful study of the matter. 2 

 If this should prove the case, it is evident that the branches which are pro- 

 vided with their own root-systems could be removed and transplanted 

 with ease. 



PROPAGATION BY CUTTINGS. 



The general conclusion suggested by the above experience was that 

 only cuttings taken from the root, or from a portion of the stem near the 

 top of the tap-root, would succeed, but as the time of my stay at Cedros 

 had drawn to a close it was not possible to direct experiments to test the 

 latter of the alternatives. Table 55, summarizing the results of my study 

 of cuttings, did not include this particular condition, which could hardly 

 have been anticipated. I early found, however, that the stem-cuttings 

 made did not respond, and that recourse must be had to cuttings in which 

 a portion of root-tissue was involved. The scheme of splitting the butt of 

 the plant so as to get two to four pieces was seized upon, the only method 

 of those used which secured positive results aside from pure root-cuttings. 



The following conclusions may be drawn from the data in table 5 5 : 



1. Cuttings involving stem-tissues alone, with a possible exception of 

 stem-tissue close to the root in seedling or rotono, do not regenerate roots 

 under the treatment given. It remains theoretically possible, by special 

 and more refined methods, to induce root-regeneration, but for the pur- 

 poses toward which the experiments were chiefly directed, this is not 

 practicable. 



2. Stem-cuttings may be kept alive, after being planted, for a con- 

 siderable period, particularly during the cooler season, by using careful 



1 Exp. 181, 182, in which either branches or whole plants were layered. 



2 I have noted the same behavior in guayule from Texas planted by me at the 

 Desert Botanical Laboratory and at Auburn, Alabama. 



