Reproduction. 67 



Jan. 6, 1908. Many buds 2 mm. long. 



Feb. 18. All but 5 plants budded. Longest leaves, 25 mm. 



Mar. 29. Little change. Longest leaves, 30 mm. 



July 28. 5 plants dead. Longest stems of new shoots, 7 cm. 



Sept. 12. 12 dead altogether. New shoots 10 to 15 cm. long. Plenty 



of flowers. Some plants have the appearance of witches' broom. 

 Apr. 3, 1909. 13 dead. Maximum stem-growth, 20 cm.; minimum, 



3 to 5 cm. New shoots in several cases killed by drought (plate 



1 6, figs. A to C). 

 Experiment 56. Station i, quadrat 2 (25 square meters). All plants cut 



off as in experiment 60, Nov. 5, 1907. 

 Jan. 3, 1908. No growth. 

 May 29. New stems (upwards of 15 mm. long, 4 mm. diameter) 



on the majority of cut stems. 



Apr. 3, 1909. Maximum growth, 10 cm. stem-length. 

 Experiment 126. Station 5, quadrat 2. Jan. 15, 1908. All plants cut 



at 15 cm. above ground. 

 May 6. Nearly all well budded. 

 Apr. 5, 1909. New shoots 10 to 15 mm. long; flowered well in 1908. 



From the rainfall data it appears conclusive that the best time to cut 

 guayule, with reference to reproduction by retonos, is just before and dur- 

 ing the rainy season. As we shall see, however (Chapter V) , this is the 

 period of active growth, and the rate at which the accumulation of rub- 

 ber takes place is such as to indicate that the practice of removing guay- 

 ule at this time is not advisable. Therefore, other considerations aside 

 (such as competition with other plants) , the removal of guayule even dur- 

 ing the most trying seasons will not exterminate the plant, except on re- 

 stricted areas which may be rehabilitated by spreading through seed. It is 

 scarcely to be doubted that even in the quadrat of experiment 1 2 1 a few 

 retonos made their appearance after the last date of observation, which, 

 unavoidably, was before the summer rains. 1 Furthermore, we are able to 

 say from observation that the conditions at this station were more rigorous 

 than at Station 2, where an earlier start was made by the retonos. 



The rate of growth of induced retonos will be seen to exceed the 

 initial growth of seedlings. The stem-growth for the growing-season of 



1908, as shown by observations taken on the above experiments in April 



1909, was upwards of 15 cm., the average amount of growth falling some- 

 where near to 8 cm. The retono in plate 9, fig. B, plant No. 10, made a 

 stem-length of 10 cm. in about three months, and would probably have 

 made more growth had it been allowed to remain. 



As between the pulling and cutting methods of gathering guayule, 

 there can be no two ideas as to the relative effect upon the rate of repro- 

 duction by means of retonos. In adjoining quadrats (experiments 114 

 and 1 1 5), in which it so happened that the same number of plants was 

 removed, in the one by cutting and in the other by pulling, the clumps 

 of retonos were as 59 to 15. This is explained by the fact that the roots 

 left in the ground when the shrub is pulled up are not only fewer in num- 



1 After this was written this quadrat was visited on April 5, 1909, and it is of 

 interest to note that the belief expressed was substantiated. See experiment 121, 

 above, on page 65. 



