THE STAMEN 



149 



The theory that peltate form is fundamental in angiosperm sporo- 

 phylls closely parallels the obsolete theory of carpel polymorphism in 

 its lack of sound morphological basis, lack of convincing evidence, and 

 continuing extension to include all appendages. 



The "Diplophyllous" Stamen. Closely related to the theory that the 

 stamen is basically so-called three-dimensional (tubular or four-angled) 

 is the tlieory that it is fundamentally double in nature, consisting of two 



Fig. 61. Diagrams to show, under the peltate theory, the origin of stamen from 

 young peltate leaf, a, peltate primordium from which develop the types h, c, d, e, 

 each with a median furrow; f to h, i to /, median longitudinal sections of a carpel 

 or stamen primordium to show two series of stages in the development of the 

 utriculate form by growth of the cross-zone meristem x. Dotted lines outline spo- 

 rangia. (After Baum, 1949.) 



united laminae. This theory is suggestive of the old idea that the angio- 

 sperm stamen represents two conifer microsporophylls, connate back to 

 back. Evidence in support of this later theory is seen largely in organs 

 transitional from stamen to petal and in so-called diplophyllous ("four- 

 winged") petals, such as occur in teratological forms in the Ranuncu- 

 laceae, Rosaceae, Saxifragaceae, and Myrtaceae. The so-called double 

 organ is four-winged, suggesting two laminae united by their mid- 

 ribs, and having a common median vascular vein. The abaxial half of the 

 double organ is seen as the true leaf blade; the adaxial half, a pro- 



