30 



PHYTOHORMONES 



sockets somewhat easier. They are fixed in rows of 12 by 

 means of brass chps which fit into grooves in a wooden 

 rack; the clips are free to move, stiffly, in a vertical plane, 

 while the holders can be rotated and thus any adjustment 

 of the growing plant is possible. 



The germinated seeds are inserted into the sockets in such a way 

 that the shoot comes under the center of the guide, and the roots point 

 downwards. The whole rack, with its 12 seeds, is then placed with the 

 roots at the surface of water contained in a zinc trough. The most usual 

 dimensions are: rack 25 X 25 X 200 mm., trough 35 X 35 X 200 mm. 

 About 48 hours after planting, the coleoptiles are 20-30 mm. long and 

 ready for use. They are selected for straightness and uniformity, and 



Fig. 9. Row of 12 Avena seedlings as Figure 8. Left to right: 

 2 intact, 2 decapitated, 2 decapitated for the second time (primary 

 leaf protruding), 2 from which primary leaf has been pulled loose, 

 2 with applied agar block, 2 showing curvature. 



since the holders are removable, rows of 12 good plants are assembled. 

 It is advisable to bring all shoots into the strictly vertical position some 

 2 hours before use (see Figure 9). 



In the preparation of the test plants the first operation 

 is to cut off the extreme tip with a razor (B, Figure 10). 

 In the subsequent period a large amount of the growth 

 hormone present in the stump is being used for its residual 

 growth, and the test plants become more and more sensitive 

 to any hormone which is applied (van der Weij, 1931). 

 After 3 hours the topmost 4 mm. of the stump is cut off 

 (C-E, Figure 10). This can be done by making an incision 



