120 The Phenomena of Morphogenesis 



experiments he concluded that polarity was a fixed and irreversible char- 

 acteristic of the plant axis and that probably the individual cells of which 

 the axis was formed themselves possessed a polar character. 



Experiments like these have been carried out on many plants. A wide 

 variety of results, often conflicting, have been reported and several 



Fig. 6-1. Polarity in willow shoots. Left, portion of a stem suspended in moist air in 

 its normal position and producing roots and shoots. Right, a stem similarly grown 

 except in an inverted position. ( After Pfeffer. ) 



theories to explain polarity proposed. Klebs (1903), for example, found 

 that roots would grow at the apical end of an inverted shoot, that water 

 stimulated root formation at any point on the twig, and that removal of 

 the bark could reverse polarity. He believed that environmental conditions 

 rather than innate polarity determined the place where buds and roots 

 develop on a stem. Vochting (1906) replied to these criticisms of the 



