THE STAMEN 



147 



Morphological Nature of the Stamen 



The basic nature of the sporophylls is discussed in Chap. 3 but is 

 further treated here in the hght of the comparisons of form and struc- 

 ture discussed in this chapter. The primitive form of the stamen is ob- 

 viously laminar, like that of the carpel. (Under the New Morphology, 

 the terete-filament type has been called primitive; the broad filament is 

 interpreted as specialized.) In ontogeny, the broader types have mar- 

 ginal meristems like those of carpels and leaves. In specialization, the 

 stamen has been modified more extensively than the carpel and the 

 laminar form largely lost. Sporangium position has also been greatly 

 modified, in such a way that two of the four sporangia appear to be 

 morphologically on the side of the sporophyll opposite its original posi- 

 tion, and all four, from an originally sunken position, appear to have 

 become superficial. But, morphologically, all the sporangia are on one 

 side of the sporophyll and are embedded in sporophyll tissues, even 

 though only lightly so in highly specialized anthers. The change in the 

 microsporangium position is largely phylogenetic, but, in some taxa, is 

 still in part ontogenetic (Fig. 57). 



The arrangement of sporangia in two pairs has been looked upon as 

 persisting evidence of ancient telomic structure, but the laminar form, 

 clearly primitive in living forms, does not support the view that the 

 pairs of sporangia represent fused terminal telomes. The vascular struc- 

 ture of the laminar stamen shows no evidence of a basic telomic struc- 

 ture. The sporangia lie in pairs between the midrib and the lateral 

 veins and have no connection with the vascular meshwork; if the 

 sporophyll consists of telomes, the sporangia should terminate vascular 

 bundles. 



Relationship of the simple and the fascicled stamen is discussed 



under androecium. 



The Peltate Stamen. In the older, descriptive literature, stamens in 

 which more or less free, dorsifixed, or versatile anthers stand somewhat 

 oblique to the filament — a common condition in highly specialized 

 anthers — were called shield-shaped or peltate, but this term did not 

 continue to be used in so simple a sense. Its revival in the early decades 

 of the twentieth century came with its use in extended and modified 

 senses. In one treatment, stamens fall in two major classes: peltate 

 (shield-shaped) and impeltate, or epeltate (not shield-shaped). In 

 impeltate stamens, the connective is the direct continuation of the 

 filament; in peltate stamens, the filament is attached laterally to the 

 anther, which usually stands at an angle to the filament. The impeltate 

 stamen is arrow-shaped if the anther sacs extend beyond the attach- 

 ment of the filament, and not arrow-shaped if the sacs do not so project; 



