BY G. P. DARNELL-SMITH. 871 



what parchment-like in texture. Shortly after, minute black 

 pycnidia are formed beneath the surface; and, breaking through, 

 form small irregular fissures or minute holes, at which points the 

 spores are discharged through the necks of the pycnidia. 



The disease almost invariably makes its appearance on the 

 sunny side of the tree, and upon that side only of the fruit which 

 is exposed to the sun. So constantly is this the case, that, in 

 an affected orange, it is almost always possible to draw an equa- 

 torial line dividing the sunny from the shaded side of the fruit, 

 and, on the former side only, will black spots be found. Even 

 on the sunny side of the tree, if the fruit is well shaded by 

 foliage, it is seldom affected by the disease, even when exposed 

 fruits around it are badly marked. 



That the rind has some principle that may inhibit the growth 

 of spores, is suggested by the incidence of the disease in the 

 various varieties of citrus fruit. It is common on the orange 

 (navel, valentia, siletta), it is found less frequently on the 

 Emperor mandarins, and quite exceptionally upon the thorny 

 mandarin. 



The infection of the fruit only upon one side of the tree sug- 

 gests that it may be related to the prevailing wind, or to the 

 effect of too much sunlight or heat upon the rind. 



The development of the disease only upon the sunny side of 

 the tree indicates that it is the sun, rather than the wind, that 

 exerts an influence. 



To test the effect of diminishing the amount of sunlight fall- 

 ing upon the trees, and to protect them from scorching winds, 

 two trees in an orchard were completely covered-in with hessian 

 in the form of a tent. They were covered in at the beginning 

 of June, that is, at the commencement of the ripening period. 



The fruit on these trees did not show black spot on the fruit 

 for two or three weeks after the uncovered ones, and then the 

 spots developed very slowly, remaining a dull brown colour; and 

 they did not pit the fruit to such an extent as fruit exposed to 

 the weather. The spots upon uncovered fruit soon become black. 

 The following season, two trees were protected from the sun by 

 putting up a screen of hessian upon the sunny side only. Here 



