128 The Phenomena of Morphogenesis 



The cause of these swellings may lie in the fact that the original tissues 

 cannot function properly under the changed orientation and that con- 

 siderable cellular rearrangement must be brought about in the new tissue 

 formed after inversion. These tumors resemble anatomically the "whorls" 

 commonly found in wound wood and consist of parenchymatous, 

 sclerenchymatous, and tracheidal elements. Vochting here has de- 

 scribed the structure of such tumors in Salix fragilis and other species 

 and believes them to be due to the innate polar tendency of individual 

 cells. On such an interpretation, the tissues are thought to twist about 

 (Fig. 6-7) until finally those of the root and of the new shoot are con- 

 nected by cells of the same polar orientation ( Kiister, 1925 ) . 



There has been considerable controversy as to this hypothesis. Maule 

 (1896) uses it to explain the behavior of cambium cells in wound wood. 



Fig. 6-7. Vessel polarity after budding. I, longitudinal anastomoses between vessels 

 in normally oriented bud and stock. II, twisting of vessels when bud has been inserted 

 upside down. At right, single vessel from the latter. (From Vochting.) 



Neeff (1922) made an extensive series of studies of the changing orienta- 

 tion of cambial cells in decapitated stems, finding that these tend to turn 

 until they become parallel to the newly regenerating axis instead of to 

 the old one (Figs. 6-8, 6-9), and he explains this in terms of the inherent 

 polar behavior of the cells, which tends to conform to that of the func- 

 tional axis. Both Jaccard (1910) and Kiister, on the other hand, disagree 

 with Vochting's explanation and attribute the changing orientation of 

 the cells mainly to mechanical factors. Twisting whorls may also appear 

 in normal callus where mechanical factors can hardly be operative. More 

 intensive studies are needed of the conditions that cause change in direc- 

 tion of cell growth. Altered direction of sap flow, for example, might 

 affect the direction of cambial cell growth in Neeff's experiments. Similar 

 changes in cellular orientation have been reported by MacDaniels and 

 Curtis ( 1930 ) in spiral ringing wounds in apple, by Janse ( 1914 ) in 

 bark strips left across a ringing wound in Acalypha, and by Tupper- 



