130 The Phenomena of Morphogenesis 



growing in a foreign substratum. Thus a root pole will fuse with a shoot 

 pole but two similar poles, when brought together, will not fuse. Vochting 

 also found that a square bit of tissue cut out from a beet root and put 

 directly back will knit in its former place but will not do so if turned 

 through 180° before being replaced there. These facts can be explained 

 by assuming that the tissues of the plant, even such relatively undif- 

 ferentiated parenchymatous ones, have definitely polar behavior. Bloch 

 (1952), however, observed that tissues of the fruits of Lagenaria do not 

 behave in this way but that plugs, cut out and replaced, will knit in any 



Fig. 6-9. Tangential sections through tissue of an axis like those in Fig. 6-8. Left, nor- 

 mal wood. Right, after decapitation, direction of cells changing to conform to the axis 

 of the lateral root, now the main one. ( From NeejJ. ) 



orientation. Microscopic examination after a few days showed normal 

 cellular fusion. 



In horticultural practice it has long been recognized that buds must 

 be placed in normal orientation on the stock if they are to knit well. 

 Colquhoun ( 1929 ) removed buds and pieces of bark in Casuarina and re- 

 applied them in an inverted position. Observation of the anatomical struc- 

 ture showed that the cells of the cambium joined freely and continued to 

 grow regardless of orientation. Wood fibers and vessels, however, show 

 the characteristic turns and twists reported by Vochting. This suggests 

 that the cambial cells are unpolarized or in a condition of unstable polar- 



