62 



Guayule. 



General Observations. 



It is generally believed that, after a field has been harvested of its 

 guayule, it will reproduce itself in a short period of years, the length of 

 which is a matter of opinion. Estimates on this point vary from 5 to 

 10 years. 1 As, however, this difference in length of reproductive period, 

 which we may call the period of rotation, involves so large an error in 

 returns on investment, an effort to get at the facts is eminently justified. 

 From the botanical point of view, the rate of reproduction and of growth 

 of desert plants has been so little studied that data bearing on these 

 questions are of great importance, especially as the eye of civilization 

 is being turned on the desert as a field in which must be developed the 

 natural resources peculiar to it. 



Normal Retoxos. 



The number of plants which arise as retofios within a given area is, 

 with probably few exceptions, small. 



Table 20. Comparative numbers of seedlings and retofios in given areas. 



These numbers are accurate as far as they go, but they do not tell 

 what proportion of all the plants of the quadrats mentioned arose as 

 retofios. In the vicinity of Station 2 plants of this sort could easily be 

 found, and all but one of those in plate 9, fig. B,were obtained in a restricted 

 area nearby, especially on the steeper slopes. But for all this, the total 

 numbers of plants which have arisen as seedlings, taking all the areas 

 into consideration, must far outnumber retono plants. On irrigated plants 

 2 years old, some 150 in number, not a single retono was observed, a 

 fact which may perhaps be correlated with the weaker development of 

 shallow lateral roots in such plants. Only one instance (plate 46, fig. B) of 

 a retono starting under irrigation has come to my notice. Numerous ad- 

 ventitious buds were distributed on the mother-root, evidently having 

 started after the plant was pollarded. This was done, not at the time of 

 transplanting, but some time later, when it was discovered that the plant 

 was not responding. The importance of normal retohos, therefore, is not 

 to be seen in the numbers but in other qualities (Chapter III). 



1 At the present writing we read in a recent number of the India Rubber World 

 (March 1909), that a new crop of guayule may be expected in " a few years." We 

 may suppose that heavily interested investors have obtained accurate information 

 upon which they base their operations, but none, so far as we are aware, have been 

 given publicity. 



