The Cultivation of Guayule. 



205 



should preferably be somewhat higher than the surface of the soil, as this, 

 in addition to enabling one to manage the shade better, prevents the dry- 

 ing out of the soil near the edge, in consequence of which the germination 

 is not so good. 



The subirrigation may be managed best by placing the trays in melgas 

 of a depth sufficient to bring the surface of the water to the level of the top 

 of the soil in the tray. In order that the water may gain free access to the 

 soil the sides of the trays must be provided with a number of holes. 



A 



Fig. 19. A, the roots of two seedlings grown in 4-square-inch paper tubes; B, ajroot-systemjof about 



... the same age, growing in a box. X9/20. 



Despite the apparent indifference of guayule seed to the temperatures 

 recorded by Kirkwood (1910a) , seeds germinate more promptly and, what 

 is more important, the seedlings make a much more rapid growth during 

 the summer months, as my experiments in July and August 1908 showed. 

 In winter, also, the seedlings were frequently killed in part by frost, in part 

 by a storm of hail, and were more subject to damping-off. The heavy 

 rains of summer also prove more or less destructive, and it was found that 

 the seedlings with the shortest hypocotyls survived the best. For this 

 reason as thin a shade as possible is desirable, the object of this being to 

 preserve the superficial soil-moisture and to cut down the light as little as 

 possible. 



