HANS BURSTROM 



47 



40 h 



10 



15 



20 

 HOURS 



Figure 2. The grand period of cell elongation with dilTercnt supplies of 

 nitrate and phosphate. 



the frequency of cell divisions are unaffected by the nitrate concentra- 

 tions above the nitrogen starvation level. Only the rate of stretching is 

 affected. Phosphorus, on the contrary, given in concentrations above 

 deficiency levels does not interfere with the cell elongation but only 

 with the cell divisions. It may be that a certain synthesis of proteins is 

 an indispensable prerequisite for cell elongation, because we do not know 

 any instance of cell elongation at present without a protein synthesis. 

 On the contrary, however, there is httle possibility that a formation 

 of cytoplasm evokes the elongation. If so, there ought to be a more rapid 

 start or a longer duration of the elongation in response to nitrogen 

 supply and resulting protein synthesis. Further, such a synthesis is a 

 characteristic feature of the meristem, and even though it continues 

 during the elongation it cannot be the cause of the incipient vacuoliza- 

 tion and elongation of the cells. Their explanation must be sought in the 

 osmotic properties of the cell or in the conditions of the cell wall. 



Elongation and Absorption of Water 



The increase in volume depends directly upon an absorption of water, 

 and thus it is necessary to consider under what conditions an uptake of 



