3o6 PLANT DISEASES 



appears first at the apex of the fruit, and inoculation 

 probably takes place through the stigma. 



GUMMOSIS OF PEUNUS JAPONICA 



(yCladospo7'mm epiphylhun^ Fr.) 



During two successive seasons a considerable number of 

 examples of the beautiful flowering shrub, Pru7ius japonica, 

 Thunb., growing in Kew Gardens, were either killed or 

 much injured by a disease agreeing in nature with w4iat 

 has been termed gummosis. Stout branches are most 

 frequently attacked ; the disease is indicated by the 

 appearance of tearlike drops of almost colourless gum 

 oozing from the branches. The drops are solitary or crowded, 

 and rapidly increase in size, eventually forming irregularly 

 nodulose masses varying in size from a marble to that of a 

 walnut. During damp weather the masses are soft and 

 gelatinous, with just sufficient consistency to hold together, 

 w^hereas in dry weather they shrink considerably and 

 become horny. Finally the masses are dissolved and 

 washed to the ground by rain. 



As already stated, the small drops are colourless, 

 gradually changing from grey to black as they increase in 

 size. If a large black mass is hardened by placing it in 

 methylated spirit, and then cut through, it will be seen that 

 the surface alone is black, the colour gradually becoming 

 lighter inwards, and white at the centre. 



This extrusion of gum is entirely due to the action of a 

 minute fungus which does not differ structurally from the 

 exceedingly common Cladosporiian epiphyllum. Repeated 

 experiments prove that the fungus is a wound-parasite, 

 saininsf an entrance into the tissues through small wounds 



