Boron Deficiency in Celery
Brittle stems and the development of brown stripes in the epidermis above the vascular bundles of the petioles are usually the first signd of boron deficiency in celery. Sometimes the brown stripes are so close together that they form a continuous line over the vascular bundles. Transverse cracks develop on the outer surface. The broken tissue curls outwards, giving the petiole a hairy appearance.
Blackened and diseased hearts are the most severe symptoms, but they are only found in stunted plants, accompanied by cracked petioles.