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Symptoms. — The leaves and fruit of trees affected with this 

 disease show small wart like exeresenees. These exeresenees 

 are of various sizes, the diameter ranging from | mm. to 1 cm. 

 (one fiftieth to two fifths of an inch), bat usually being from 1 

 to 1 mm. They sometimes run together and cover a large 

 portion of the leaf or fruit. In case the fruit is attacked while 

 still very young the tissues below the wart grow more rapidly 

 than normally. This causes the fruit to become covered with 

 bumps, of irregular pyramidal shape. These grow propor- 

 tionately with the fruit and on the mature fruit may sometimes 

 be 1 to 2 cm. across and project out nearly the same distance. 

 At first the warts look like small semi-translucent pimples, of 

 a slightly lighter shade of green than the surrounding healthy 

 tissue. In a few days if the weather be favourable, the waits 

 become prominent, assume a conspicuously light green colour, 

 and look watery. After this they become covered with a 

 delicate fungus, which is at first grey, then dusky, and at last 

 black. Finally the infected tissue covering the tips of the 

 warts is cut off from the healthy tissue below by a formation 

 of cork, and ultimately the cork formation becomes so abun- 

 dant as to give a clingy white colour to the old warts. The 

 appearance and development of the warts are much the same 

 on the leaves as on the fruits. There is no formation of a 

 lump below the wart. When the leaves are attacked while 

 still very young much the same effect is produced as in the 

 case of the fruit, the leaf surface bulging abruptly outward and 

 causing the warts to appear seated on hollow conical pro- 

 tuberances. The leaf is often considerably thickened where 

 the wart is situated, and the persistence of the leaves for at 

 least a year in most cases, enables the cork formation to proceed 

 further than is usually the case on the fruit. 



Varieties of Trees Attacked. —Scab attacks only certain 

 species of citrus fruits, the sour orange (Citrus bigaradia) being 

 particularly subject to its ravages. It was first noticed in the 

 United States on this host Both leaves and fruits of affected 

 trees are often severely injured. The greatest loss, however, 

 is caused by its disfiguring the lemon. It attacks the fruits 

 far more frequently than the leaves, and by causing the lemons 

 to become bumpy and warty renders them valueless or nearly 

 so. On the foliage it is never abundant enough to do serious 



'V 



harm. After the sour orange and lemon, the Satsuma oran 

 is most frequently attacked. This variety, probably a form of 

 Citrus nobilis, came from Japan. On this host scab rarely 

 causes serious damage to the crop, and is seldom seen in the 

 foliage. In all probability the disease was introduced from 

 Japan into the United States on this orange, in several 

 localities in Florida the first appearance of scab on the sour 



