46 PLANT GROWTH SUBSTANCES 



shortened, which results in a reduced cell length* and an over-all in- 

 hibited growth in roots. These two actions can manifest themselves 

 simultaneously in one root, which supports the idea that there are two 

 different processes going on in the cell elongation. 



The first phase above all deserves attention in this connection. We 

 may find there the primary cause of the cell stretching, whereas the 

 ensuing growth by intussusception may be assumed to follow only as 

 a consequence of the preparation made during the first phase. 



Cell Elongation and Proteins 



It is wrong to assume, however, that this is all that takes place during 

 the elongation. Frey-Wyssling (7) has especially emphasized that there 

 is a considerable increase in the amount of cytoplasm during the cell 

 stretching. That this is so in elongating coleoptiles and anther filaments 

 is less significant because they lack a meristem, but the same holds true 

 in roots as shown by Miss Kopp (9). It is correct that the increase 

 up to 90 per cent in volume is caused by water intake, but nevertheless 

 as much as half of the protein synthesis takes place during the cell 

 elongation. 



That there is some connection between proteins and elongation is to 

 be seen from the fact that an increase in the supply of nitrogen increases 

 the rate of cell elongation, whereas no such effect is found, for instance, 

 with phosphorus (4). Table i shows what happens when excised wheat 

 roots are supplied with increasing amounts of these two nutrients. High 

 concentrations of nitrogen increase the root length. Analyses have veri- 

 fied that an increasing supply of nitrogen leads to increased synthesis 

 of proteins. See Figure 2 for the rate of cell-elongation increases. Note 

 that the time of starting and the duration of the elongation as well as 



TABLE I 

 Growth of isolated wheat roots with different phosphate and nitrate supplies 



Increase in Increase in 



Solution root length Cell length cell number 



MM. fi longitudinally 



Low P, low N 13. 7 ±1.7 177 ±3 35 ± 4 



High P, low N 25.5 ±2.0 170 ±3 120 ±5 



Low P, high N 25 . 2 ± 1 . 3 269 ±4 5 1 ± 3 



