37 



The destruction of the leader in various trees is followed by the 

 formation of one or more new leaders from terminal laterals which 

 assume the functions of the one destroyed. In such cases a j^lagio- 

 tropic organ becomes an orthotropic organ, and what holds true for 

 various trees is characteristic of many plants both as regards primary 

 and secondary organs, etc. 



The effects of continual pruning of branches on the growth of 

 leaders is well illustrated in forests. Where pine or chestnut trees 

 are grown close together the lower limbs are being continually 

 pruned by natural agencies. The result is a tall, straight shaft with 

 a limited crown, whereas when these trees are growing unrestricted 

 in the open their branches remain intact and they develop freely 

 causing the tree to become thick and stocky, and present quite a dif- 

 ferent aspect from those grown in close proximity to one another. 

 On the other hand, the constant pruning of leaders causes an accel- 

 erated growth of branches causing them to elongate and thicken up. 

 The cutting of the leader of a cucumber plant induces the growth of 

 axillaries, and pruning the axillary shoots at certain places not only 

 increases the amount of fruit in certain axils but it restricts the fruit 

 to certain desirable positions. Naturally, however, in the cucumber 

 plant axillary shoots are produced in abundance and it is seldom 

 necessary to manipulate the leader to induce their growth. Some- 

 times, however, they do not form in each axil and then it becomes 

 necessary to resort to the cutting of the leader in order to induce 

 them to grow. Heading in a secondary organ has the same effect 

 on tertiary organs as the cutting of primary organs has on secondary 

 organs. For example, the heading in of an axillary of the cucumber 

 plant induces fruit to set more abundantly at certain points. It also 

 induces new leaders or tertiary shoots to form on secondary organs 

 or branches. This in turn affects the formation of fruit. Or, in 

 other words, the fruit can be concentrated on the cucumber plant in 

 certain desired positions thus obviating the unnecessary spreading 

 of the vines over a large area. 



Since the fruit cluster of the tomato plant corresponds to a second- 

 ary organ, and since the pruning of primary organs induces the great- 

 est effect on secondary organs, the cutting of the leader would 

 stimulate the growth of fruit. On the other hand, cutting of the 

 axillary shoots, branches and leaves (secondary organs) induces a 

 greater growth in the length of the stem. 



