DETECTION AND QUANTITATIVE DETERMINATION 25 

 2. DETECTION OF GROWTH SUBSTANCE IN POLLEN. — A mixture 



of pollen and 1 cc. water, weakly acidified with acetic acid, may be 

 applied in a small chamber around the stump of a decapitated 

 coleoptile. Growth may be measured interferometrically (Fig. 

 28) (Laibach and Kornmann, 1933a) or in any other suitable 

 manner. Pollen mixed with agar (weakly acidified) may be cut 

 into blocks and applied unilaterally to intact coleoptiles (Laibach 

 and Kornmann, 1933a). Pollen may be suspended in lanolin by 

 mixing thoroughly in the proportion of 50 mg. air-dried pollen, 

 1 cc. water (weakly acidified), and 1 g. anhydrous lanolin. The 

 mixture may be applied to various kinds of test objects, where it 

 will induce bending (Fig. 37) : intact or decapitated coleoptiles, 

 epicotyls of Phaseolus multiflorus, aerial roots of various species, 

 petioles of Coleus, etc. This method of preparation and applica- 

 tion is very useful because the growth substance is given off into 

 the plant very slowly, and the lanolin does not dry out (Laibach, 

 19336). 



3. DIFFUSION OF GROWTH SUBSTANCE INTO AGAR. — Went 



(1928a) demonstrated that growth substance would diffuse out of 

 decapitated coleoptile tips if the latter were allowed to remain 

 standing on 3 per cent agar blocks for approximately 2 hours 

 (Fig. 8A). Since this method was first described, growth sub- 

 stances have been "diffused" out of numerous other plant parts. 

 The agar blocks are then applied unilaterally to decapitated 

 coleoptiles as described above. Details of Went's procedure are 

 to be found under the discussion of quantitative determination. 



4. DIFFUSION OF GROWTH SUBSTANCE INTO DEXTROSE AGAR. 



Boysen Jensen (19336) found that it was impossible to obtain 

 growth substance from roots by standing the decapitated root 

 tips on 3 per cent agar, but satisfactory demonstrations were 

 made possible by the use of a dextrose salt agar of the following 

 composition: 3 g. agar, 10 g. dextrose, 0.1 g. calcium nitrate, 

 0.025 g. potassium monohydrogen phosphate, 0.025 g. magnesium 

 sulphate, a trace of ferric chloride, and 100 cc. water. The 

 agar blocks must be made up fresh the day that they are to be 

 used, and this is done most easily if 10 cc. of the agar mixture is 

 spread out upon a warm glass plate (size 10 by 10 cm.). Blocks 

 can be cut from this by using parallel knives; the size of the 

 blocks used is 2 by 2 by 1 mm. Upon such blocks root tips of 

 Zea mays or Vicia Faha are placed for 2 to 4 hours ; the blocks are 



