130 MORPHOLOGY OF THE ANGIOSPERMS 



pollen grains then lie in a common chamber, from which they are shed 

 through a single opening. Early breakdown of the wall occurs occa- 

 sionally — Berberis, Nuphar, and some orchids. The two pollen masses 

 may mingle or lie side by side without separation by sterile cells — 

 Cassia, and some poricidal anthers. In the union of the two sporangia, 

 the tissues of the entire separating wall or of some part of it disinte- 

 grate and are largely absorbed. The adjacent outer anther wall, above 

 and beside the separating wall, is commonly also involved in the disin- 

 tegration; the outer anther-sac walls are retracted, and the intermingling 

 pollen is shed through a large opening. In some taxa, the separating 

 wall persists almost to the outside of the anther, and the chambers dis- 

 charge through a common break which opens separately below into the 

 two chambers. Often the pollen forms a mass which fills the furrow 

 between the two sporangia. The details of opening vary greatly, espe- 

 cially the extent of retraction of the anther walls, which may even com- 

 pletely invert the chamber. The variations depend, at least in part, upon 

 the extent of the fibrous layer and the thickness of the anther wall. The 

 double character of the chamber is usually evident externally as well 

 as internally, but the chamber may appear simple in late stages. 

 Sporangium fusion is uncommon in anthers with latrorse dehiscence. 

 Union of sporangia is probably always between an "outer" and an 

 "inner" sporangium — the two that belong morphologically together on 

 the laminar sporophyll. The association of the lateral pairs is obviously 

 close, morphologically as well as histologically, and refutes the view 

 that two sporangia are abaxial and two adaxial and the theory that, 

 morphologically, the anther represents two conifer sporophylls "back 

 to back." 



Unusual Forms and Arrangements of Stamens 



Unusual forms and arrangements of stamens that suggest splitting, 

 forking, and branching received much attention from 1850 to 1900 and 

 are still occasionally discussed. Chorisis, dedouhlement, and multiplica- 

 tion of anthers were considered methods of origin for supposedly 

 branched stamens. Today these terms are little used, even in taxonomic 

 descriptions, and have long had morphological implications that are, at 

 least in part, false. 



The stamen is fundamentally a simple, unbranched organ, as shown 

 by the primitive genera Degeneria, Eupomatia, Austrohaileija. Many of 

 the so-called branching forms can now, with the aid of anatomy and 

 comparison with the stamens of related taxa, be interpreted more ac- 

 curately than formerly. Longitudinal division ("splitting") of the stamen 

 occurs in some taxa, as in the Mai vales, but, in other taxa, the ap- 

 parent division represents partial connation of two or more stamens. 



