THE ANGIOSPERMAE 



1171 



all united to the style, and between which protrudes the large, flattened stigma. 

 Orchis, and many other genera, have only one stamen, with two pollen- 

 bearing lobes, the back of which is fused to an upgrowth from the top of the 

 inferior ovary, probably representing the third lobe of a tripartite stigma, 

 the two lower lobes of which remain functional. The united structure 

 stands up prominently in the centre of the flower (see Chapter XXX). 

 Another well-known case is that of the large genus Aristolochia (Fig. 1140), 

 in which the anthers are united in a ring around the outside of the stylar 



Fig. 1 140. — Gynosteniiuni in Aristolochia. A, Perianth re- 

 moved showing anthers dorsally attached to the style. 

 B, Flower in longitudinal section. C, Flowers in position 

 on the plant. (After Van Tieghem.) 



column, to which they are dorsally fused, their enlarged connectives often 

 surmounting the stigma. A similar condition is characteristic of the family 

 Stylidiaceae, where there are only two stamens, their filaments being com- 

 pletely adnate to the style, and the anthers standing beside the stigma. 

 Examples of cohesion between stamens and superior ovaries are much less 

 frequent, but one striking case is Gymnotheca (Fig. 1141), a genus nearly 

 related to the Pepper family, in which the six stamens are united to the 

 ovary wall, nearly to its top. In Passiflora the stamen filaments are adnate 

 to the gynophore but the anthers are below the level of the ovary. 



The cohesion of stamens with each other is a widespread feature of 

 flower structure and occurs in all degrees, from simple pairing to union of 

 all the stamens into a tube, or to a comparatively elaborate grouping into 

 fascicles or bundles. The phenomenon bears the general name of synste- 

 mony. Besides occurring in a great number of isolated cases it is a general 

 characteristic of some large families like the Papilionaceae, Malvaceae (Fig. 

 1 142), Rutaceae, Meliaceae, Guttiferae, Cucurbitaceae and Compositae. In 

 the last named family cohesion is by the margins of the anthers, the filaments 

 remaining free, but in the generality of cases it is the other way about, the 

 filaments cohering while the anthers are free. 



A succession of stages may be observed in Cucurbitaceae, between 

 flowers with all five stamens free and those in which all five are closely 



