252 TRANSLOCATION IN PLANTS 



more rapidly. It is conceivable, however, that within the phloem tissues 

 leading to a dominant part, such as a pollinated fruit, there may be more 

 active protoplasmic streaming than in those leading to the suppressed 

 part, such as fruit that has not been pollinated. Therefore, although the 

 actual gradient may lead to the suppressed fruit, the higher activity within 

 the conducting tissues leading to the other may in effect bring about a 

 steeper gradient to the dominant fruit. It is also possible that the dominant 

 part may be more effective in removing the material from the transporting 

 tissue. Data on gradients leading to fertilized and unfertilized cotton bolls 

 show no difference in gradient but a marked difference in rate of receipt. 

 This would indicate a more effective transport system. The reverse gradi- 

 ent for reducing sugars is greater in the fertilized bolls, which indicates 

 that they have a greater ability to accumulate sugars. A transport mechan- 

 ism of the sort proposed by Miinch can theoretically be adapted to account 

 for many phenomena of dominance, regeneration, and growth correlation, 

 but much of the available evidence points to an active movement in a direc- 

 tion the reverse of that required by the theory. There are also several other 

 weaknesses in the hypothesis. A transport mechanism based on diffusion 

 and streaming protoplasm seems well adapted to account in part for domi- 

 nance of one part over another, for observed phenomena of regeneration and 

 growth correlation as well as for other phenomena of behavior. 



There are some phenomena bearing on food movement and utilization, 

 however, such as the influence of gravity, which though not definitely in 

 opposition to any theory of transport, yet are not easily explained by any 

 of the theories. That some substance or condition other than supply of 

 carbohydrate and mineral elements is involved in growth and regeneration 

 phenomena is demonstrated especially by the unexplained behavior of 

 cambial growth. Some of the growth responses following ringing are 

 undoubtedly due to an interruption of the transport of foods and mineral 

 elements. It is also possible, though it seems not conclusively established, 

 that some responses may result from an interruption of the transport of 

 specific substances of the nature of hormones. There is also evidence that 

 such cutting may alter normal electrical gradients and it may influence 

 the transmission of stimuli. 



