129 



In very severe cases of blight the trees succumb so suddenly that 

 the leaves do not fall, but simply wither and turn brown on the twigs. 

 This is also frequently the case with a single branch. In such cases 

 the trees usually die outright in a few weeks and never put out any 

 new growth from the trunk. Again, a single branch may wither as 

 suddenly. In the great majority of cases, however, a vigorous new 

 growth pushes out from the trunk at the beginning of the rainy season 

 and at first it would seem as though the tree would recover. Some- 

 times such sprouts continue growing vigorously two years or more, 

 but sooner or later they show small and usually yellowish leaves and 

 begin to decline. Often, too, such shoots wilt and show all the symp- 

 toms of a fresh case of blight. Ordinarily the tree continues to decline 

 gradually and is finally removed before it dies, to make place for a 

 new tree. Again, cases may linger ten years or more, making a 

 slow sickly growth, and even bearing a little fruit. Cases of real re- 

 covery from genuine blight are, however, almost entirely unknown, 

 although hundreds of growers have been deceived by the vigorous 

 growth of water sprouts sent out by blighted trees after the first 

 wilting. 



A most remarkable fact is that the roots of blighted trees invariably 

 seem to be entirely healthy. The vigorous growth of water sprouts 

 they support shows that they are capable of considerable functional 

 activity. 



No anatomical features which are characteristic of blight have yet 

 been found. Under the highest powers of the microscope the tissue of 

 every organ of blighted trees appears to be normal, which is in strik- 

 ing contrast to foot root and die-back. The physiological activity of 

 the leaves and branches, however is very much deranged, „^as has been 

 proved by experiments on the loss of water from blighted twigs. 



Varieties of trees attacked. — Almost all citrus fruits are attacked by 

 blight, although some sorts are nearly exempt. Common oranges 

 (Citrus Aurantium), tangerines and mandarins ( CUrm nobilis), and 

 grape fruit [Citrus decumana), in about the order named, are the most 

 susceptible. Lemons blight less than any of the fruits mentioned, 

 while limes and sour oranges, especially the latter, are almost exempt 

 from this disease. Certainly not more than one sour orange tree in a 

 thousand is blighted even in regions most liable to the malady. Cu- 

 riously enough, the sort of stock used appears to have no influence in 

 increasing or diminishing the susceptibility of trees to the disease. 

 Common oranges budded on sour orange roots are apparently as liable 

 to blight as are sweet seedling trees. 



Situations most liable to the disease. — Although blight attacks citrus 

 fruits growing on all kinds of soil, it is most common on trees growing 

 on very light, sandy hammock (^). Such soils are usually com- 

 posed almost whoUy of sand with an admixture of decaying vege- 

 table matter; sometimes, however, they are underlaid at a depth of from 

 4 to 12 feet with clay or hardpan (sandstone). Trees growing on clayey 



(1) Hammock land ii that which was originally covered with hard woods, es- 

 pecially live oak, magnolia, hickory, etc. 



