DISEASES OF LIME AND OTHER CITRUS TREES 219 



spots are commonly surrounded by a narrow yellowish band 

 or zone. In the more advanced stages, the surface of the spots 

 becomes white or greyish, and finally ruptures, exposing a 

 light brown spongy central mass. Old spots soon become 

 overgrown by saprophytic fungi, and may appear pink or 

 black on account of these fungus growths. 



" On the fruits the spots are very similar to those formed 

 on the leaves. They do not penetrate far into the rind. They 

 may be scattered over the surface, or several may occur 

 together forming an irregular mass. Gumming is sometimes 

 associated with the spots formed on the fruits. Canker, 

 apparently, does not cause a rot of the fruits directly, but opens 

 the way for other fungi to enter and cause infected fruits to 

 rot. The spots on young twigs are like those on the leaves 

 and fruit. On the older twigs they are more prominent, and 

 more or less irregular in shape. This is specially true of old 

 spots. They show the same spongy tissue that is found in 

 the spots on the leaves, but assume a cankerous appearance 

 and the surface membrane completely disappears. These 

 spots or cankers are formed in the outer layers of the bark 

 tissue, and do not penetrate to or kill the wood. The spots 

 once formed in the bark are persistent, and are not readily 

 sloughed off. They may remain for a long time and form 

 centres from which infections may readily spread. This was 

 confirmed by observations on infections produced on spotted 

 trees in the greenhouse, and in the grove by artificial infection. 

 Some of these spots have been under observation for over a 

 year, and show no tendency to slough off." 



R. A. Jehle in a later account emphasizes the diagnostic 

 value of the translucent, glazed, oily appearance of the zone 

 immediately next to the ruptured portion of the spot. This is 

 lacking from scab, which moreover distorts the leaves and causes 

 warty projections on the fruit, characteristics which are absent 

 from canker. Scaly-bark spots are hard and glazed, those of 

 anthracnose are sunken. 



SusceptihUity. 



It has not been established that any citrus plant is quite 

 immune from canker, but wide gradations in susceptibility 

 occur. From the Philippines it is reported that the common 

 lime, which is presumably the commercial lime of the West 

 Indies, is highly susceptible, while a variety known as the Tahiti 

 lime seems practically immune. 



Effects. 



The direct losses due to the disease result from its effects on 

 the fruit. The rind is more or less covered with the canker 



