Young banana plant (about 6 months old) showing severe symptoms of Panama disease. The younger leaves show progressive yellowing, followed by necrosis (death), starting from the leaf margin. The older leaves have collapsed.

Older banana plant (2-3 years old), showing yellowing and death of some of the older leaves. Meanwhile, young shoots (s), known as "suckers", emerge from the underground corm. Most of these suckers are removed, but one is left to produce the next season's flowering stem when the main stem is cut down after it has produced fruit. Suckers also are used as planting material to establish new banana plantations. However, if the plant is diseased (as in this case) the plant will almost always die before the fruit matures, and if the suckers are used as planting material they will spread the disease to other sites.

Older banana plants showing advanced stages of Panama disease; note the "skirt" of dead leaves hanging down on each plant.

Even later stages of disease, but apparently healthy suckers are growing from the corms. The infection will spread into these eventually.

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Elm tree in mid summer, showing advanced stages of Dutch elm disease - thinning of the tree canopy, and browning of the leaves. Photograph taken in Cambridge, 1972.

The same tree about 2 months later, showing almost complete loss of leaves. The elm trees nearby are still healthy.

Elm tree outside the author's office, in Edinburgh, summer 1998. This tree began to show symptoms of elm disease in the spring, and the disease is now in a progressive stage. This whole line of elms along the front of this building was felled soon after the photograph was taken, to help prevent spread of the disease.

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