Several symptoms of various leaf malformation are associated with boron deficiency. "Hook leaf", which consists of a single or double hook on the pinnae near the tip, and transverse corrugations on the pinnae are usually the first symptoms to appear. Fasciation and the inability of pinnae to expand are associated with more severe deficiency. The leaf tissue is very fragile and the leaflets break easily, resulting in the condition known as leaflet shatter. Incomplete development of the pinnae, which develops as a tuft of bristles at the terminal end of the frond - "blind leaf" - is also a symptom of boron deficiency. The development of extremely small, thin pinnae - "fishbone leaf" - is a sign of very severe deficiency. The breakdown of the growing point resulting in a dry heart rot can be expected as a final characteristic symptom.

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