72 Guayule. 



done to increase their productivity is still a question for experimental 

 determination, but seeding in favorable years by means of seed from 

 densely grown areas would be distinctly beneficial. The importance of 

 seed is so great that in the harvesting of shrub the practice of leaving 

 large plants for the purpose of producing seed should in all circumstances 

 be initiated. As a practical question of economics, the difficulties of 

 time and distance in the desert are so great, not to mention those arising 

 in connection with climatic irregularities, that any attempts to better 

 conditions over wide areas are fraught with expense which may not be 

 considered as warranted by those interested. 



COMPARATIVE ABILITY TO GERMINATE IN THE FIELD. 



The ability to germinate promptly, to attain a condition of physio- 

 logical resistance, is of prime importance to desert plants, and very much 

 more important to them than to plants which are more favorably placed 

 with reference to water-supply (Ganong, 1907; Lloyd, 1909a). So far as 

 the question of germination is concerned the evidence is not forthcoming 

 that desert plants exhibit more indifference to initial water-supply than 

 others (Livingston, 1906). For the rest, as for further elucidation of 

 this problem, much comparative study is necessary. There seems to be 

 little doubt, however, that the rate at which physiological resistance is 

 acquired and the amount of this resistance are very different in different 

 plants. For example, the seedlings of many succulents soon acquire 

 the characters of the parents, the cacti (Ganong, 1898) being notable 

 examples of this. This must be of no small weight as a factor in enabling 

 young plants to withstand the rigors of drought, though this very cir- 

 cumstance in the cacti opens them to the attacks of animals (MacDougal, 

 1 910), so that millions of seedlings are eaten, affording both food and 

 water to desert animals. 



As has been shown, and as will be further developed in the following 

 chapter, the guayule seedling offers no exception to the rule that desert 

 plants need an abundance of water during the period of germination. 

 Observation in the field indicates further that marked readiness in ger- 

 mination is not in any way indicative of adaptation to desert conditions. 

 A field test of the germinating ability of guayule in comparison with 

 that of alfilaria (Station 7, May 30, 1908, exp. 139) showed that about 

 3 per cent of the seed of the latter germinated, while about 0.2 or 0.3 per 

 cent of guayule succeeded in getting a foothold in the same place under 

 the same conditions. These figures are probably too low for both plants, 

 inasmuch as ants were observed carrying off seed on each occasion that 

 the station was visited. This test, however, may indicate the direction 

 in which research may contribute toward the explanation of the success 

 which the alfilaria has had in invading desert territory. 



A further observation was made at Camacho, on the Mexican Central 

 Railway, on the Hacienda de Cedros, a point for the shipment of guayule, 

 where a stack-ground, had been kept supplied with shrub from the neigh- 

 boring region. It is customary to bring in the shrub in loose bundles on 

 the backs of burros or in carts of various sizes and kinds to these ship- 

 ping-points, there to be made up into bales for handling on the railroad. 



