64 DISEASES OF CULTIVATED PLANTS 



Bitter-pit in apples. This disease is of a physiological 

 nature ; the cause is unknown. It is known by the appear- 

 ance of small brown spots in the flesh, most abundant at the 

 calyx end of the fruit. The spots are at first most abundant 

 just under the skin, but by degrees extend deeper into the 

 flesh. After the outermost brown spots have existed for 

 some time the tissue collapses, and the skin sinks at those 

 points, so that the surface of the calyx end of the fruit presents 

 the appearance of small-pox markings. I have investigated 

 diseased apples from South Africa and from Australia, and 

 the disease is probably present in greater or less quantity 

 wherever apples are grown. A section through a brown spot 

 shows the protoplasm dead and brown in the cells, and the 

 starch is present in quantity, although it has disappeared 

 entirely from the surrounding normal tissue that has be- 

 gun to ripen. It is perfectly certain that the disease 

 develops during transit in apples coming to England from 

 South Africa, Australia, etc., and the calyx end of the fruit is 

 most seriously injured, in fact in the majority of instances it 

 is confined to that portion. So far as experiments have been 

 made, the nature of the soil has no marked effect, neither has 

 the absence or presence of manure of any kind tried. The 

 general symptoms suggest the local presence of some substance 

 that kills the cells, and prevents the transformation of the 

 starch into sugar. The brown substance has sometimes, but 

 not always, a bitter taste. 



Massee, Kew Bulletin, 1096, p. 193 ; 1097, pp. 142 and 250. 



'Spot' disease of orchids. The very prevalent disease 

 known to cultivators of orchids as ' spot ' is characterised by 

 the presence of somewhat sunken, brownish spots or patches 

 on the leaves, and although the general health of the plant is 

 not, as a rule, materially affected, except when the spots are 

 especially numerous and encroach on each other, forming 

 large blotches, its general appearance is unsightly. The 

 disease commences as minute pale spots on the upper surface 

 of the leaf, and may be crowded or scattered, and the fact 

 that very young leaves are frequently spotted, has been 

 considered as strong evidence in favour of the disease being 

 due to some parasitic organism. This, however, is not the 

 true . explanation, and a series of careful observations and 

 experiments, described in detail elsewhere, prove conclusively 



