Secretory tissues of the flower of Sanango racemosum (Gesneriaceae). I. Light microscopy

Sanango racemosum (Ruiz & Pav.) Barringer has a dry stigma without a free-flowing secretion fluid but with a hydrated proteinaceous pellicle. The stigmatic surface is covered with unicellular, bottle-shaped papillae. At maturity, a viscous emulsion is accumulated between the cuticle and the pecto-cellulosic wall of the papillae, causing it to become detached from the surface of the papilla cell walls. The style has a central solid core of transmitting tissue. The cells of the transmitting tissue are rich in starch and exhibit thick lateral walls rich in pectic substance. The nectary disk is a ring elongated into a cup, with five lobes at the top. One of the most conspicuous histological features of the disk is the abundance of starch in the secretory cells. The disk is supplied only by phloem; the stomata are found in the top of the lobes. A fluid substance is produced just before anthesis and secreted through the stomata with no visible decline in starch level. During anthesis and after fertilization, a rapid decline in starch is observed. The hypothesis that the disk has other functions besides that of a nectary is discussed.