PLANT HORMONES 



153 



in the cells which are elongating or those that are fully grown. 

 These regions are described in Chapter 5. Embryonic cells 

 grow by increasing the amount of protoplasm, but elongation 

 is largely the result of swelling by increasing the amount of 

 water which forms large vacuoles. 



A 



A 



A 



2 3 4 12 3 4 12 3 4 



Demonstration 



B 



C E 

 Detection 



A 



Collection 



LJmM 



L M 



K 



V 



□ LJ 



P 



N 



Polar iransporf 



Fig. 24. Auxin (its concentration in the agar is shown by various shades of 

 dotting) and growth of Avena coleoptiles. 



Ufper left. Demonstration of auxin formation by coleoptile tip. Plant No. 1 is 

 left intact; Nos. 2, 3 and 4 are decapitated. On No. 2 the cut tip is replaced; on No. 3 

 auxin (in agar) is stuck. The right hand set of four plants shows the effect of this 

 treatment on growth after three hours. 



Lower left. Collection of auxin from cut coleoptile tips. For a period of two hours 

 6 coleoptile tips are placed (H) on a layer of agar, 6x8x1 mm. (G). After removal 

 of the tips the agar contains auxin diffused out of the tips, and is cut into 12 blocks (I). 



Upper right. Scheme or test method for auxin. Coleoptile (A) is decapitated 

 leaving the primary leaflet (B). The latter is partly pulled out (C and D) and an agar 

 block with auxin is placed on one side of the cut surface of the coleoptile (E). Two 

 hours after application of the agar the resulting curvature (F) is measured. 



Lower right. Demonstration of polar transport of auxin. On the apical surface of 

 a coleoptile cylinder cut from the seedling (K) a block of agar with known auxin concen- 

 tration is placed and the basal surface is placed on a block of pure agar (L). A few 

 hours later the greater part of the auxin will have been transported towards the lower 

 block (M). If the coleoptile cylinder has been reversed (N and 0) no transport what- 

 soever is detectable; all auxin remains in the upper block, in contact with basal cut 

 surface (P). (From The Botanical Review, vol. 1, pp. 162-182. By F. W. Went, 1935.) 



