pearls or pearl glands, small, spherical nodules that develop on the surface of vine stems, petioles, and the underside of leaves along the large veins. They form under warm humid conditions, such as in a glasshouse, and when the vine’s growth is exuberant. They are a multicellular outgrowth of the epidermis, even to the extent of an occasional stoma, but collapse to a rusty colour and disappear when the humidity drops.
© Jancis Robinson and Oxford University Press 1994, 1999, 2006, 2015
