DETECTION AND QUANTITATIVE DETERMINATION 19 



ture of 22 to 22.5°C., and after 72 hours the seedUngs are ready for 

 use; they are then 25 mm. long on the average. 



Went (1928a) used plants grown in water culture. After the 

 preliminary treatment mentioned above, they are transferred to 

 the darkroom and allowed to remain in the germinating dishes 

 until the seedling roots are a few millimeters long. They are 

 placed then in glass holders over zinc or glass trays of water, as 

 indicated in Fig. 7. At a temperature of 25°C. and relative 



Fig. 7. — Diagram illustrating the water culture method of growing Avena 

 seedlings as test objects for making growth-hormone determinations. The oat 

 seedlings are supported in glass holders held in brass clamps; these fit firmly into 

 slots in a wooden block. The roots of the seedlings dip into a tray of water. 

 Orientation of the coleoptiles may be accomplished by adjusting the positions of 

 the brass clamps and glass holders. {Modified from Went, 1928a.) 



humidity of 90 per cent, the coleoptiles are ready for use after 

 about 30 hours. 



Each of the methods described has its advantages and dis- 

 advantages, which must be evaluated at the time when a partic- 

 ular experiment is contemplated. Culture of the seedlings in 

 \dals may facilitate working with indi\'idual plants but increases 

 the number of manipulations when many tests are being made. 

 Difficulty is encountered in properly orienting the coleoptiles for 

 uniform application of the plant parts or agar blocks to be tested. 

 The fixed position of the seedlings in the soil or sawdust, which 

 raises this difficulty, turns out to be an advantage if much 



