120 NUT GROWING 



very secure in most nut trees for the first year or 

 two. If the stock were to send out great thrifty 

 natural shoots in a hurry in order to make a large 

 top for replacing the one that was cut away, these 

 large heavy shoots might drop off by their own 

 weight. The tree seems to be aware of that fact 

 and may perhaps send repressive hormones to the 

 root asking root enzymes not to hurry the top growth 

 until the latter has become firmly united. In former 

 years botanists held that what is called axial polarity 

 or, in other words, the direction of sap movements 

 in the long axis of the tree was due to the flow of 

 materials for making shoots in the top part of the 

 tree. They held that the flow of materials for mak- 

 ing root was sent from the top down below the 

 ground. The accumulation of these materials for 

 building purposes in opposite ends of the tree was 

 supposed to be responsible for the phenomena of 

 polarity and regeneration. Loeb, has shown, how- 

 ever, that we must take into the problem a new fac- 

 tor, that of the formation of a special hormone in 

 the end bud part of a shoot. This hormone exerts 

 repressive influence upon the growth of other shoots 

 below that point. It perhaps influences the degree 

 of root development as well. The matter rests upon 

 a chemical basis. The hard wooded hickories seem 

 to be wiser than the chestnuts in their habit of re- 

 pressing root action until the top is secure. The 

 chestnuts send out enormous new growth before 

 making top buds and coming to rest. These massive 

 chestnut tops occasionally blow off in moderate 



