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Pomona College Journal of Economic Botany 



On the Tzvigs. (Fig. 16) : The twigs on the Havana Sweet orange 

 trees at Santa Paula often died back as far as did the leaves, but in most 

 cases they first remain green but bare for some time after the leaves have 

 been killed and dropped. Fig. 10 shows a branch nearly four feet long 

 which was entirely killed on the tree before the leaves dropped. This 

 condition is especially true of the smaller outside twigs on the orange trees. 

 This dying is accompanied by the same unhealthy discoloration described 

 in the leaves, the tissues dividing the dead from the healthy portions as- 

 suming the characteristic brown ring. No spores appear upon the twigs 

 until after they have been dead for some time and are subjected to a moist 

 condition. In the moist chambers of the laboratory the fruiting bodies were 



Figure 17. Spots caused by wither-tip on lemon; the same on orange to the right. 



produced upon all of the dead tissues (Fig. 16) and upon the apparently 

 healthy green portion of the twigs 12 inches below the ring, showing that 

 the disease was working back all of the time and simply awaiting a con- 

 dition favorable for another outbreak. 



The twigs of the lemon trees do not succumb to the attacks of the disease 

 as rapidly as do those of the orange. They remain bare for a long period, 

 and though green and healthy-looking do not bear leaves or fruit. So 

 far as worth to the tree is concerned they might just as well be dead. In time 

 they do turn brown and slowly die from the tips back, the infection usually 



