Bleeding canker. Liquid exuding from the trunk of a horse chestnut tree (Aesculus hippocastanum). This pathogen destroys bark, cambial tissue and the phloem (sugar conducting tissue). If this damage spreads round the trunk then more general effects will be seen, namely yellowing of leaves, early leaf fall, failure to fruit and damage to the crown of the tree. Research suggests that a bacterium may be responsible. The disease affects trees ranging in age from young saplings to mature trees. It is estimated that some 35,000 to 50,000 trees are already infected over a widespread area. Photographed in Regent's Park, London, UK.