T'l.AXT Diseases in the Western Province. * 529 



At various spots on the surface of the affected fruit, the under- 

 lying tissue bursts through the epidermis, giving' rise to a very dis- 

 figuring wart-like excrescence on the fruit up to about one-sixteenth 

 of an inch in diameter, and the same in height. The tissues in the 

 immediate vicinity of the wart become hard. 



This disease, known as Lithiasis, is not caused by any parasitic 

 organism, but is of a physiological nature, and occurs in pears of 

 certain varieties more particularly in dry years, when the trees are 

 in soil which is not rich in plant foods, or which suffers from certain 

 disabilities such as, perhaps, lack of drainage. I am told that the 

 block of trees in question was not given adequate drainage i-iintil last 

 winter. It wall be recalled that last season was a particularly dry 

 one, and this doubtless accounts for the prevalence of the disease 

 then. 



Black Mould, a Storage Rot or Soft Pruits caused by 

 Rhizojnis nigricans Ehr. 



One of the common causes of storage rot in soft fruits in the 

 Western Province is the mould Rhizopu.'i nigricans Ehr. This mould 

 is considered to be a strict wound parasite, that is, it can only gain 

 access to a fruit and cause its rot through an injury of some sort 

 in the skin; a few tentative inoculation experiments carried out with 

 the spores of this fungus in the laboratory here, indicate that the 

 injury need only be very minute. 



The fungus, to the naked eye, appears as a thick mould on the 

 surface of the fruit. The growth of the fungus in the interior of 

 the fruit precedes the formation of superficial mould, with the result 

 that surrounding the black area one finds a brown zone about half an 

 inch wide without a growth of mould on the surface. The spore- 

 bearing organs, or sporangia as they are called, are produced on 

 comparatively long stalks, the sporangiopliores, and are visible as 

 minute spherical black bodies ; each sporangium might be likened 

 to a hollow sphere on a stalk with a cap fitting over the top half of 

 it. The sphere is known as the Colwinella, and the spores are formed 

 in the space between its wall and the cap. The spores are liberated 

 by the breaking- up of the cap, while the columella is left intact. This 

 is shown in figure 1, a, which shows a group of three sporangio- 

 phores, the one on the left has not yet liberated its spores ; the one 

 in the centre has just done so; that on the right shows the columella 

 only (magnified 47 diameters). The figure marked 6 is a single 

 sporangium magnified 167 diameters, and shows the columella y, x 

 the line of union between the columella and the sporangium wall 

 proper, and z the contained spores: figure 1, c, shows three spores 

 magnified about 1060 diameters. 



As far as actual size is concerned, a sporangium which is only 

 about one two-hundred-and-fiftieth part of an inch in diameter, 

 probably produces anything from 1000 to 1500 spores, each spore 

 being only about one two-thousand-five-hundredth part of an inch 

 long. 



This mould was first brought to my notice in a consignment at 

 Stellenbosch of magnificent peaches of the Sea Eagle variety, packed 

 for export. The consignment showed such a high percentage of waste 

 due to this mould, however, that it had to be disposed of locally. 



