THE GUAYULE 325 



rived at an economic maximum. It may then be concluded that as- 

 suming an even stand of a ton to the acre, it requires 15 acres to supply 

 one ton a year, allowing for good years and bad. Most guayule land 

 will not yield so well. It is, however, clear that where the land is very 

 cheap and can be used for other profit to a considerable extent without 

 materially damaging the shrub, a conservative method of gathering 

 could have been made to yield reasonable and constant returns. 



It has been assumed that the stand is maintained by the reproduc- 

 tion of guayule by seed. Field studies have shown that this is true. 

 Areas of known dimensions have been cleared of all plant growth, and 

 the new seedlings counted; and censuses have been taken of such areas 

 to determine the population of plants of various ages. The information 

 obtained proves clearly that the more usual method of reproduction is 

 by seed. It must be added that different localities often not widely 

 separated show a very diverse efficiency in this regard. Indeed, it has 

 often been difficult to see any evidence that if the present growth were 

 removed there would be any effectual replenishment by seed. Such places 

 are marked by the absence of small seedlings and usually carry only ma- 

 ture individuals of approximately the same size. But it by no means 

 follows that in such situations there is no reproduction at all, for in ad- 

 dition to seedlings the guayule also increases its members by means of 

 " retofios," that is, by new shoots which strike upward from the shallow 

 lying lateral roots. In the course of time retofios establish their own 

 roots and become entirely separated from the rest of the plant and con- 

 sequently independent organisms. Retofios grow more quickly than 

 seedlings and are more certain of arriving at maturity. Because of the 

 previous establishment of the root they may develop where, on account 

 of slight depth of soil, seedlings would fail. As a matter of fact they 

 are relatively more plentiful on rough stony ground and are particularly 

 prone to occur where the surface of the ground is steep and the roots 

 become exposed by erosion, though this is not a condition necessary to 

 their formation. Furthermore, they develop flowers in the first season 

 of their growth so that, in the event that the guayule were removed they 

 would constitute a pretty certain insurance against extinction. 



Whether the cutting away of the aerial portion of the plant induces 

 the growth of retofios or not has not been decided, but, as already said, 

 it is followed by abundant reproduction of new shoots from the stocks 

 left in the soil. These follow cutting in about 40 per cent, of the cases, 

 so far as determined, but as the year when the censuses were made was 

 a dry one the figure is probably low for a good season. The time when 

 the cutting takes place doubtless also influences the result. Aside from 

 this, however, these new shoots develop rapidly, but flower abundantly 

 in the first season and are thus effective in reseeding the ground. 



We see, therefore, that the guayule is by no means unequipped for 



