74 Guayule. 



territory around Jimulco, for instance, as many as 50 young plants have 

 been found around full-grown trees." But, on the other hand, speaking 

 of the occurrence of young plants in supposedly very unfavorable spots, 

 Endlich explains this by saying that "it is likely that they have been 

 developed from such seeds as were either stamped into the ground by 

 goats (as these animals are the ones which commonly graze in the guay- 

 ule territories), or had been dropped by these animals and thus found 

 favorable conditions of development in the animal excrements. It 

 would, in fact, be difficult to find any other explanation for the enormous 

 growth of the guayule plant in small, isolated places (having usually 

 the size of the resting-places of the herds of goats) * * * ." 



As to the supposedly favorable conditions afforded by animal excre- 

 ment, it may well be doubted that these are more so than the soil itself 

 affords. Experiments have shown that soil at all rich in humus derived 

 from manure is distinctly unfavorable for healthy germination. Even 

 "garden" soil at Cedros, with no addition of manure, is less favorable 

 than the unaltered lime-charged soil of the normal guayule habitat (plate 

 16, figures D and E). Even after thorough leaching from exposure the 

 possible advantages are hardly important, and, at all events, in such 

 situations the seeds and seedlings have no advantage of shade, as the 

 herding-spots of goats are usually bare of vegetation. Nor can the 

 stamping into the soil by these animals have any value, as the seeds ger- 

 minate well only with very shallow soil covering, as much as 2 mm. 

 depth being enough to show a marked decrease in germination. 1 It would 

 seem, therefore, that if Endlich's observations are correct as to the occur- 

 rence of guayule seedlings in such situations, it is safe to infer that the 

 rainfall conditions are, on occasion, such as to make ready germination 

 and early growth possible for a good percentage of seeds even in open 

 bare spots where no advantage of shade is offered. My own observations, 

 at any rate, sustain this view. Experiment 139 (see p. 72) is a case in 

 point, and the results were supported by general observation during the 

 summer of 1 908, when there was a fairly generous if not a maximum field- 

 germination. The net result of this season is indicated by the numbers 

 of seedlings observed in April 1909 (see p. 70). These are known to 

 have germinated at or during the growing-season of 1908, and had suc- 

 cessfully sustained prolonged drought till the time of observation. At 

 no other point was there seen a better crop of seedlings at the age of 

 these, and they germinated without the least protection, as the quadrat 

 had been completely denuded. 2 



Nevertheless, when seedlings are observed in the field at other than 

 favorable seasons, it is frequently noticed that the larger numbers are 

 in the protective shade of other plants; but this is not peculiar to the 

 guayule alone. The explanation, we believe, is not that the guayule 

 seedling is ombrophile, but that the eliminating effect of the drought 

 period subsequent to a period of germination is more drastic elsewhere 



1 Kirkwood, 19 10. 



2 By contrast, it should be said that at Station 1 only very few seedlings 

 were found on a large area denuded of all plants save small guayule. As goats 

 had been pastured here, however, it is impossible to draw any conclusions. 



