78 



Guayule. 



TABLE 30. Growth of seedlings (all unbranched) which germinated about June i, 

 1908; collected April 3, 1909. Station 2, quadrat 7, 100 square meters. 



TABLE 



It will be seen that the average maximum amount of growth for the 

 whole of the growing-season of 1908, as indicated by the data obtained in 

 April 1909, is 8.5 mm., stem-length. This, however (as shown by table 

 28), is less than the amount determined by the measurement of seedlings, 

 germinated in 1908 but collected on September 8 to 12 of that year, 

 namely, 14.8 mm. The difference in favor of the earlier collections may 

 perhaps be explained by the fact that care was not taken to take every 

 seedling in a given area. To do this requires a minute search, which was 

 given only in April 1909. It is not improbable also that other seeds 

 germinated later in the season, though this is not likely. It is therefore 

 safer to conclude that the average amount of growth in length of the 

 epicotyledonary stem for the season of 1908, taking all seedlings into con- 

 sideration, is not more than i cm. If we should consider only those which 

 germinated at one time, at the beginning of the growing-season, this 

 amount would probably turn out to be somewhat greater. Under the 

 conditions for the period in question the maximum amount of growth 

 was 5.5 cm.; the minimum, 1.5 mm. Seedlings of these dimensions, and 

 two illustrating the average growth of 281 seedlings (Station 2, quadrat 

 4) , are reproduced in plate 1 7 , fig. A. Measurement of the main shoot alone 

 throws out of account the growth of branches, so that a fuller conception 

 of the amount of development possible for a seedling under natural con- 

 ditions may be had only by seeing the plants themselves. 



