Polarity 125 



expressed in the location of regenerating structures in leaves is determined 

 by anatomical structure. Behre (1929) reports that regeneration in the 

 leaves of Drosera is apolar. 



There has been much discussion as to whether, in the higher plants, 

 polarity once established can be reversed. It has been the common ex- 

 perience of botanists and horticulturalists that cuttings in which the apical 

 end is put into the soil will not do as well as those with normal orienta- 

 tion. Some inverted cuttings are found to take root, however, and may 



^ Proximo I 



Ditto I 



INTACT ROOT 



ROOT SEGMENTS REGENERATION 



Fig. 6-4. Polarity of regeneration in root of Taraxacum. A root segment produces shoots 

 at the proximal end ( next the base of the plant ) and roots at the distal end, whether 

 the segment is normally oriented, horizontal, or inverted. Compare with Fig. 18-17. 

 ( From Warmke and Warmke. ) 



live thus for some time. Kny ( 1889 ) successfully grew cuttings of Hedera 

 and Ampelopsis inverted for several years, and Graham, Hawkins, and 

 Stewart ( 1934 ) did so with willow cuttings, which were still nourishing 

 after 11 years. The tips of weeping willows will often root at the apex 

 if they are dipping into water (Pont, 1934). Such inverted structures, how- 

 ever, often show external malformation and anatomical distortion. Growth 

 may become normal again if the cutting is restored to its upright orienta- 

 tion and can form roots at the morphologically basal end. Lundegardh 



