18 GROWTH HORMONES IN PLANTS 



Culture Methods. — Whether the Avena seedlings are grown in 

 soil, sawdust, or water culture, the preliminary treatment is about 

 the same. The glumes may or may not be removed for soil or 

 sawdust culture; the seeds are soaked in water for 2 to 4 hours, 

 after which they are placed in petri dishes on moist filter paper 

 and allowed to remain for about 36 hours. (If illuminated for 

 a few hours at the beginning the first internode remains short.) 



For Boysen Jensen's soil-culture method, the seeds are removed 

 from the petri dish and placed in glass vials, 20 by 100 mm., filled 

 with screened, sandy garden soil (Fig. 6). The soil should be 

 well-watered so that no further watering will be necessary but not 



Fig. 6. — Curvatures produced by placing Avena coleoptile tips unilaterally upon 



decapitated coleoptiles. 



too wet, for the plants then become less sensitive. Each vial 

 contains but one seed, and 25 to 30 \'ials are held together by an 

 elastic band. These are moved into the darkroom and placed 

 in a petri dish, then covered with a small bell jar so that the air 

 will remain saturated. Under the usual conditions in the dark- 

 room at a temperature of 21 to 21.5°C., the coleoptile appears in 

 two days. Then the bell jar is removed, and the coleoptiles 

 continue their growth under low-humidity conditions for 24 hours. 

 In this time they attain a length of 15 to 25 mm. and are ready for 

 use. 



Navez and Robinson (19326) planted the seeds with glumes 

 removed in sterile, purified, maple sawdust contained in glass 

 vials 15 by 25 mm. The sawdust retains about 4.3 times its 

 weight of water. The seed is planted dry, embryo side upward, 

 and inclined about 10 deg. from the vertical. The end of the seed 

 away from the embryo may or may not be allowed to protrude 

 slightly above the level of the sawdust. In this method, germina- 

 tion is allowed to proceed in a light-tight chamber at a tempera- 



