86 



Guayule. 



Age and Height. 

 For the purpose of controlling the above conclusion I have, as clearly 

 as possible, made estimates of the ages of plants of various sizes, making 

 no assumption as to the rate of growth, but being guided solely by the 

 marks in each individual. The results are compiled in table 39. 



These data have been charted in the accompanying curves, corre- 

 lating age and height (fig. 15, upper diagram). It is an obvious objection 

 to the value of these curves that they are based, necessarily, on compara- 

 tively few plants, but their value is enhanced by the individual treat- 

 ment, since the estimate of age was made with great care. A fairly close 

 correlation emerges, however, from the diagram, from which we see that 

 plants of 10 years of age have a height of about 30 cm., and those of 15 

 years about 40 cm. 



An increase in height of 10 cm. over 30 or 35 cm. is correlated (judg- 

 ing from the data of table 39) with a doubling at least of the weight 



