6 Plant Tissue Culture 



istic of every fragment, irrespective of size, and 

 hence by implication of the individual cells (1878, 

 329, 1884, 329) . Thus, the distal portion of a stem 

 or piece of stem always produced leaves and the 

 proximal portion roots, but whether a given cell 



Fig. 1. Tubers of Corydalis solida, cut and allowed to regen- 

 erate. The tissues at the center of the tuber form leaves (left), 

 roots (center), or merely wound callus (right), depending on the 

 spatial orientation of the cut, showing the dependence of morpho- 

 genetic expression on fortuitous external factors. (From Goebel, 

 K. 1908. Einleitung in die experimentelle Morphologie der 

 Pflanzen. 220, fig. Ill, 293.) 



