MYCOSPHAERELLA 217 



Cucumber and tomato canker. Dr. Grossenbacher has 

 recently described a disease caused by Mycosphaerella 

 citrullina (Grossenb.), which has proved destructive to melons 

 in the United States. The presence of the disease is in- 

 dicated by the wilting of the leaves first, then the entire 

 plant. The nodes of the skin, especially those on the lower 

 part of the plant, are of a waterlogged or oily-green colour, 

 with or without an exudation of gum. At a later stage these 

 diseased patches become dark and gummy, or dry and grey, 

 depending upon the quantity of gum present. Most infections 

 are confined to the nodes, and when the patches have been 

 in existence for some time, numerous minute blackish peri- 

 thecia are present. Infection experiments proved that the 

 parasite can enter uninjured tissues of melon plants. Pump- 

 kins or vegetable marrows, water-melons, and certain other 

 cucurbitaceous plants were also proved to be susceptible to 

 the disease, but curiously enough cucumber plants proved 

 quite immune, and resisted all attempts at infection. Two 

 forms of fruit are produced by the fungus ; first a conidial 

 form, known as Diplodina citrullina (Grossenb.), and as 

 Ascochyta citrul/itia (C. O. Smith). This is followed by the 

 ascigerous form of fruit, Mycosphaerella citrullina (Grossen- 

 bacher). 



During the early summer of 1909 I received several inde- 

 pendent consignments of diseased tomato plants from the 

 neighbourhood of Waltham Cross, Mx., showing in every 

 case a canker-like disease attacking the basal portion of the 

 stem, for a distance of two to four inches in length, commenc- 

 ing from the ground line. The lower nodes of the stem also 

 sometimes showed diseased pale spots. The diseased portion 

 of the stem was shrunken and the cortex considerably broken 

 up by the mycelium of the fungus present, which proved on 

 examination to be the Ascochyta, or conidial form of the 

 fungus, causing melon wilt. The minute perithecia of the 

 fungus were very abundant on the broken up tissues of the 

 stem, and were present even for some distance on the under- 

 ground portions. Tomato plants attacked as described above 

 soon wilt and die. Within a week after the receipt of the 

 diseased tomato plants, a specimen of a diseased cucumber 

 plant was received at Kew for examination from Gloucester- 

 shire, which showed the characteristic whitish blotches at the 

 nodes of the stem, described and depicted as attacking melon 

 plants in the United States, and on examining the fungus, 



