THE STAMEN 



129 



of the primitive laminar stamen to latrorse and to the elaborated ex- 

 trorse and introrse of advanced anthers. The presence in the same taxon 

 and even in the same flower of extrorse and introrse dehiscence is evi- 

 dence that these types represent ecological adaptations. Dehiscence in 

 laminar stamens is necessarily simple and determined directly by 

 sporangium position. In advanced anthers, sporangium position is not 

 simple; phylogenetic shifting has brought the outer members of each 

 pair to the side opposite that of their original position, and the resulting 

 obliquely inward or out\vard dehiscence is derived, secondarily ex- 

 trorse or introrse. Both extrorse and introrse dehiscence have apparently 



Fig. 57. Diagrams and a sketch of cross sections of anthers showing modification in 

 form of connective at time of flowering. A, B, Iris pumila, by differential growth: 

 A, young, B, mature; C, D, Ntjinphaea colorata, by cambium-like growth, develop- 

 ment of ridge on connective: C, young, D, mature. (A, B, after Engler; C, D, after 

 Kaussniann. ) 



been developed in some taxa from ancestrally simple extrorse — Laura- 

 ceae — and from ancestrally simple introrse — Magnoliaceae except for 

 Liriodendron. Latrorse dehiscence similarly has two origins. It is clear 

 that extrorse and introrse dehiscence do not necessarily indicate deriva- 

 tion from ancestral forms with abaxial and adaxial dehiscence, respec- 

 tively. The terms must be considered as chiefly of descriptive value. 



Union of Sporangia. In the primitive stamen, the sporangia lie close 

 together in lateral pairs; in advanced stamens, they remain so or have 

 been broguht even closer together by reduction of intermediate laminar 

 tissues. In many families, they unite laterally by breakdown of the 

 separating wall, usually late in ontogeny, as the pollen matures. The 



