Pomona College Journal of Economic Botany 



29 



descriptions pointed to wither-tip as we saw it in Ventura County, and the 

 matter was followed up as carefully and as fully as time would permit. 

 The results were that under the trees were to be found quantities of the 

 discolored leaves so common to the attacks of this disease, while the familiar 

 leaf spot was seen everywhere. Bare twigs and dead branches showing me 

 acervuli (fruiting bodies) were also very common. Perhaps not all of 

 the dropping of the young fruit, referred to, was caused by wither-tip. but. 

 from the indications, it is more than likely that a great loss was due to it. 

 Even the indications in the discolored leaves, leaf-spots and bare twigs 

 are interesting from so dry a country as Arizona and only goes to show 

 that the disease may thrive and do well in any climate where there is 

 a rainy season. 



In California. In this state the disease may be found in practically every 

 citrus growing section, but it is not contended that it has been doing damage 

 in all. In Ventura County, the writer has collected specimens of the leaf- 

 spot in all parts, including those sections furtherest away from the coast. 

 As stated before the fungus seems to thrive best in the vicinity of Santa 

 Paula in spite of the fact that lemon groves are situated much nearer the 

 coast and are subject to more cold and dampness at Oxnard than at this 

 place. Xo serious attacks on the orange trees have been noticed at Ventura 

 which is situated right on the sea border. 



DESCRIPTION 



On the Leaves. (Figs. 15 and 16): The presence of the fungus 

 is best told by its appearance on the leaves. The most common forms are 

 leaf-spots which show up while the leaves are still clinging to the tree and 

 appear to be healthy in every other way. The spot is usually light brown 

 to nearly colorless and is surrounded by a very characteristic brown ring, 

 which separates the dead from the living tissues of the leaf (Fig. 16). Arising 

 upon the dead discolored spot are numerous minute dark acervuli ( fruiting 

 bodies of the fungus). The spots may begin at any point of infection and 

 spread so as to run into each other almost entirely destroying the texture 

 of the leaf. They may start at the tip-end or at an edge and cut out deep 

 margins. It appears that this condition is brought about by the fact that 

 after the infection started the leaf was able to retain enough vigor to 

 resist the attacks, so that the diseased areas only were killed, instead of 

 the entire leaf succumbing and falling off as is usually the case. 



This latter form is perhaps the most common indication of wither-tip on the 

 lemon trees. The leaves first turn a sickly yellow color, gradually become 

 brown and fall to the ground. Many may fall while still in the yellow state, 

 while large numbers have been collected and the wither-tip obtained from 

 them, which were still green when they fell. Not a few leaves may be found 

 which begin to turn brown at the tip (Fig. 15) the infection working backwards 

 to cover the entire surface before the stem is reached and severed. 



On the sweet and navel orange-trees the infestation is very marked and 

 sudden. The leaves die, curl up and turn a greenish-brown color while 



