Mechanisms of Cell Elong-ation 



HANS BURSTROM 



General Course of the Cell Elongation 



THE mechanism of cell elongation can be viewed from different 

 angles: as a hormone problem, or as a question of morphologic 

 and metabolic changes of the cell. Invited to read a paper on the 

 mechanism of cell elongation, I should like as far as possible to avoid 

 discussing hormones and hormone actions, and concentrate upon the 

 course of the cell elongation. In its general features this problem recently 

 has been awarded an excellent treatise by Frey-Wyssling (8) in a growth 

 symposium paper, but when growth is considered in connection with 

 hormones, the crucial point is not only to find out what happens during 

 the elongation but to find the real inciting cause of the process, where 

 the hormones are fikely to exert their action. 



Many opinions have been advanced for the cause of the cell elonga- 

 tion, and there is scarcely any part of the metabolism that has not 

 been assumed to form the point of action of auxins and connected with 

 the elongation. Therefore the title, "Mechanisms of cell elongation," 

 obviously covers such a wide subject that I must restrict myself to 

 certain aspects of the problem only. 



The superficial cytological course of the elongation has proved to be 

 rather similar in roots and shoots, although these are different with 

 respect to their physiological behavior. Figure i shows some well-known 

 main features of cell elongation. The example is taken from the elonga- 

 tion of the epidermis of roots. Growth follows the usual S-shaped curve 

 with a very slow start. The increase in length of the cell is in this case from 

 about 1 8 to 300Ai, and, as is well known, the increase in volume involves 

 largely an absorption of water. Of the osmotic properties the suction 

 pressure of the cell can be determined easily on elongating cells, and this 



