208 CONTROL MECHANISMS IN CELLULAR PROCESSES 



rate. We call this effect "stored growth," since it is as if the growth 

 which would have occurred if the inhibitory treatment had not been 

 given, is stored up and makes its appearance, adding onto the ex- 

 pected growth rate, when the inhibition is removed. 



We have studied the stored growth effect more extensively using 

 15 per cent Carbowax 4000 (w/v), which inhibits growth nearly 

 completely but causes relatively negligible osmotic shrinkage (for 

 reasons we do not understand), which complicates the interpreta- 

 tion of the results with mannitol. The stored growth effect does not 

 appear to be a passive osmotic swelling, because it can be inhibited 

 by KCN, whereas osmotic swelling and shrinking is not prevented 

 by KCN. The most clear-cut effect is obtained if a Carbowax-inhib- 

 ited section is transferred to Carbowax plus 10~^ M KCN and, after 

 several minutes to allow KCN inhibition to take effect, to KCN in 

 water. A negligible expansion occurs. When transferred then to 

 water, after the usual lag of several minutes for abatement of KCN 

 inhibition, the rapid stored growth rate appears and continues until 

 the section reaches about the length it would have attained had no 

 inhibitory treatments been given. This indicates further that the 

 stored growth effect is not an alteration of the cell wall which be- 

 comes lost upon KCN treatment; KCN just temporarily prevents 

 its appearance. Furthermore, we were surprised to find that KCN 

 treatment itself, of sections growing in water, gives rise to a com- 

 parable stored growth effect, in which case also osmotic changes 

 could not be involved. On the other hand, we have not noticed any 

 stored growth effect in sections treated with auxin, for example, the 

 KCN treatments in Fig. 7-2. 



There may be some relationship between the stored growth effect 

 and the "residual effect" described by Cleland, mentioned above. 

 He interpreted the inhibitory effect of KCN on it as indicating that 

 there had occurred a plastic "loosening" of the cell wall which was 

 being maintained by metabolism and became lost if metabolism was 

 inhibited by KCN. As noted above, this does not seem to fit the 

 behavior of the stored growth observed by us. 



We were struck by the fact that the growth rate observed during 

 the stored growth response is generally of the magnitude which 

 would have been expected had auxin, rather than the inhibitory 

 treatment, been given. We tend to think that this has some con- 

 nection with the fact that stored growth has not conspicuously ap- 



