152 MORPHOLOGY OF THE ANGIOSPERMS 



Nectaries 



Nectaries are surface areas, emergences, or organs where nectar is 

 secreted. Floral nectaries are, morphologically, of two types: localized 

 areas where nectar is secreted, or organs transformed from their original 

 form and function. Nectaries that are modified organs may have re- 

 stricted secretory areas or be secretory over most of their surface. 

 Secretory areas, such as those on the receptacle, may be superficial only 

 or may be proliferated, forming emergences that suggest organs. Re- 

 duced organs, most commonly stamens or petals, are often represented 

 by nectaries. These nectaries may have extensive secretory surfaces — 

 some of the Proteaceae — or only minor nectariferous areas — Coptis and 

 Salix. Superficial nectaries may be minor or major areas on organs other- 

 wise largely normal — Aquilegia, Ranunculus, Viola. Septal glands, nec- 

 taries on the abutting and partly connate walls of carpels in syncarpous 

 gynoecia, are perhaps the most elaborate of superficial nectaries. They 

 are characteristic structures of many Liliaceae, Amaryllidaceae, Palmae, 

 Bromeliaceae. Where the carpels are not fused by their external edges, 

 the nectar is excreted along a slitlike lateral or distal opening. Where the 

 marginal areas are fused, the nectar flows out through a tubelike pas- 

 sage to a small aperture on the top of the ovary. Direction of dehiscence 

 of anthers is biologically correlated in insect pollination with position 

 of nectaries: extrorse where the glands are below the stamens, introrse 

 where they are above the stamens. 



Histologically, the secretory tissue of a nectary consists of subepi- 

 dermal, small, closely packed cells, with rich cytoplasmic content. 

 The epidermis overlying this tissue varies in structure; rarely, its cells 

 also are secretory. A cuticle, usually thin, is commonly present, al- 

 though nectaries without a cuticle have been reported. Stomata, usually 

 with enlarged openings, through which the nectar exudes, are present 

 in many nectaries. In other nectaries, the nectar diffuses through the 

 epidermis and cuticle. Rarely, a nectary may consist of a secretory area 

 in the epidermis alone, where the cells are papillose or replaced by 

 multicellular hairs. 



The morphological nature of nectaries can best be determined by 

 comparisons with the flower structure of related taxa and by anatomical 

 structure. The number, origin, and type of vascular bundles supplying 

 them give important and usually definite evidence of their nature. The 

 traces of nectaries that represent organs are few and well defined; the 

 vascular supply of superficial nectaries is diffuse, with many minor 

 bundles from several or many points of origin, which may be on more 

 than one floral organ; for instance, on receptacle and ovary, on stamen 

 and petal. The nature of nectariferous discs, especially ring-shaped discs, 



