August 1, 1913.] 



THE INDIA RUBBER WORLD 



563 



Notes on the Acclimatization and Cultivation of the Guayule 



(Parthcnium Argentatum Gray.) 



By Francis E. Lloyd, MacDonald Professor of Botany, McGxll Unkrrsily, Montreal, Canada. 

 A PAPER READ AT THE THIRD INTERNATIONAL RUBBER CONFERENCE, HELD IN NEW YORK, 1912. 



SINCE the time when, as a result of the then probable prejudice 

 to the natural supply of guayule shrub, the problem of its 

 cultivation was attacked, the question as to : What changes in 

 the responses of the plant might be expected on the increase of 

 water supply — has been uppermost. An answer has been obtained 

 as yet only in general terms, and, from the practical point of 

 view of the guayule rubber manufacturer, it is less satisfactory 

 than from that of the plant physiologist. Indeed, in searching 

 for a complete answer, the time clement is so great that a number 

 of years is required for working out satisfactory data. Those 

 available to the present writer have been obtained from plants 



Professor Francis E. Lloyd. 



grown for two seasons at Cedros, Zacatecas, Mexico ; for three 

 seasons at Tucson, Arizona, from material derived from Cedros, 

 and from the Stockton plateau, Texas ; from a single plant grown 

 by Dr. H. H. York, at .Austin, Texas, also from Stockton plateau 

 material. At Auburn, Alabama, plants have been grown both in 

 the open and in the glasshouse, both from Cedros seed and from 

 Texas stocks, for three years. Seedlings two years old, grown 

 in Tucson, have also been available. 



The information based upon the above material will be briefly 

 presented in what follows. The situations indicated include the 

 semi-arid Chihnahuan and Sonoran deserts — within the former of 

 which the guayule has its natural habitat — the moister climate of 

 Eastern Texas, and the relatively wet region of middle Eastern 

 Alabama, which has a rainfall of 45 to 55 inches. Before con- 

 trasting the plants from these widely different places we may 

 profitably compare those growing naturally within the proper 

 area of distribution. It has already been shown* that the guayule 

 is by no means uniform in structure within this area, the differ- 

 ences being such as may be referred to differences in the amount 

 of available moisture, which may in turn be attributable either to 

 greater rainfall or to the character of the soil, chiefly mechanical. 

 The structural differences referred to are those of relative thick- 

 ness of the "bark," or, more properly speaking, the cortex, these 



•Publication 139, Carnegie Institution of Washington. 



being such that, the greater the available water, the relatively 

 thinner the cortex. 



Correlated differences in the length of the annual accretions of 

 stem are to be noted. The more rapidly grown stems display a 

 greater tendency to obvious shrinkage of the cortex, so that, in 

 place of the rounded surfaces of the slowly-grown stem, longitu- 

 dinal corrugations are to be seen. I am creditably informed that 

 such characters are displayed by the guayule from the eastern- 

 most region of its distribution area, in the State of Nuevo Leon, 

 to an extent so marked that the practical extraction of crude rub- 

 ber is reduced, roughly speaking, to about 4 to 5 per cent, on mill 

 weight. This may not necessarily be taken to mean that the 

 amount of rubber relative to the volume of the rubber-bearing 

 tissues is less than elsewhere, but that the volume of woody tis- 

 sues (wood, hard bast, etc.) is greater. Nevertheless, this may 

 be the case, and I know of no studies which have been made to 

 settle the point. But, in the light of what we do know about the 

 relation of water supply to the amount of rubber secreted, it is 

 not improbable that the actual intracellular secretion in these 

 Nuevo Leon plants is somewhat less than in dryer regions. 



The well-known habital differences between the so-called 

 "macho" and "embra" guayule furnish another case in point. 

 Macho guayule is sparingly branched, has thick "bark," and the 

 younger branches shrink little on drying, and, at all events, do 

 not show longitudinal wrinkles. Embra, on the other hand, is 

 very much branched, the younger twigs become furrowed on 

 drying, and the bark is relatively thin. In the former the 

 flowering shoots are sharply delimited from the leafy shoots ; 

 in the latter, the embra guayule, they are not. Whether these 

 two tj'pes represent racial differences or not I do not care 

 to discuss here, but it is well known in Mexico that, from the 

 practical point of view, the distinction is important, as macho 

 guayule is considered distinctly better as regards rubber content. 

 Since both types may be found associated in the same locality it 

 seems improbable that the intracellular secretion is unequal in 

 them, but that the inferiority of the embra is due to the greater 

 relative volume of the woody cylinder, and the relatively greater 

 number of smaller branches. It is significant that when guayule 

 of any type is put under cultural conditions, and supplied with 

 abundance of water, the habit of the plant swings away from the 

 macho toward the embra type of growth, in that there is a tend- 

 ency for the leafy shoots to run out into flower stalks, and toward 

 the greater development of wood. 



These tendencies are to be seen whether the plant is grown in 

 the desert under irrigation or in regions of higher rainfall, and are 

 a summation of differences in minor details which I have treated 

 more fully elsewhere. Of these I need mention but one, and that, 

 in general terms, to the effect that the greater the water supply, 

 up to the limits thus far observed, the greater the rubber-barren, 

 fibrous or woody tissues in volume and in hardness, the greater 

 the irregularity of growth, and the larger the number of smaller 

 twigs and of leaves. This condition is one which presents diffi- 

 culties to the manufacturer of guayule rubber due to the greater 

 relative volume of the bagasse, and this will obtain wherever the 

 plant may be grown with an abundant water supply. In speak- 

 ing of acclimatization, therefore, we may aroid, for the purpose 

 of this paper, further description of the tissue development. It 

 will suffice to confine attention to the rate of growth, tenure of 

 life and the total amount and rate of rubber secretion. 



TENURE OF LIFE. 



When a plant is removed from its own to another habitat, the 



