CITRUS FRUITS 129 



to some extent by rectifying the unfavourable condi- 

 tions of the soil, but is best controlled in the packing 

 houses by the use of a disinfectant in the washer : one 

 pint of formalin to 1250 gallons of water or one pound 

 of permanganate of potash or copper sulphate to 625 

 gallons of water. 



Black Rot. This disease or fruit rot has been 

 reported from South Africa by Mr. I. B. Pole Evans, 

 and the organism causing it described by him under the 

 name of Diplodia natalensis. He describes the disease 

 as follows : 



The first evidence of disease is a translucent or watery 

 appearance of the rind, usually around the stalk end of the 

 fruit. This is quickly followed by a softening and gradual 

 brown discoloration of the affected tissue. The brown dis- 

 coloration, when it has once appeared, spreads very rapidly, 

 and uniformly over the whole fruit, which then becomes 

 distinctly sticky to handle, while at the same time a greenish- 

 brown liquid exudes from it where it comes into contact with 

 anything on which it is resting. Very soon after this a dark 

 olive-green to black discoloration appears at the stalk end, and 

 from thence encroaches over the whole fruit until it is con- 

 verted into a black mummified mass with a very crinkled and 

 shrivelled surface. 



Fruit in this condition left exposed to the dry atmosphere 

 soon dries out, and remains indefinitely a hard body exceedingly 

 light in weight, but retaining to a considerable extent its 

 original form and shape. The loss of weight in the fruit can 

 be detected almost as soon as the brown discoloration appears. 

 When a dry lemon is cut open the whole of the pulp has been 

 absorbed, and nothing remains but a dark fibrous mass of 

 tissue. 



The pips and radiating septa are usually covered with a 

 dull greyish growth. On examining the lateral black discolora- 

 tion more closely with the naked eye or with a hand lens, it is- 

 seen to be due to the formation of a nufnber of small dark 

 patches under the epidermis of the rind. As these dark masses 

 increase in number they run one into another and coalesce, so- 

 that the whole surface takes on a homogeneous dark colour. 



If affected fruit is kept under moist conditions, a very 

 different state of affairs occurs. The surface very soon becomes 

 studded with innumerable tufts of hyphae, at first greyish - 

 olive in appearance, but which later on turns darker coloured ,. 



K 



