THE ANDROECIUM 103 



connation. In the Caryophyllaceae, obdiplostemony is incomplete; tran- 

 sitional stages in union of whorls are numerous. In the Saxifragaceae, 

 both diplo- and obdiplostemonous taxa are present, with whorls separate 

 or fused. 



Evidence supporting the reduction theory — loss of the outer whorl 

 of stamens — is strong. Polystemony is generally accepted as primitive 

 and diplo- and haplostemony as advanced. (The story of simplification 

 in the flower is one of progressive shortening of the receptacle and 

 dropping out of whorls.) Stages in reduction of whorls in the androe- 

 cium are readily seen in some families — Lauraceae, Caryophyllaceae, 

 Saxifragaceae, Primulaceae, Sapotaceae, Myrsinaceae, Theophrastaceae. 

 Most genera of the Primulaceae are diplostemonous, but, in Samolus 

 and Naumburgia, the outer whorl of stamens is represented by rudi- 

 ments; in some species of Primula, the outer whorl, usually absent, may 

 be present in normal form. 



Objection has been raised to the interpretation of obdiplostemony as 

 brought about by loss of a whorl of stamens, on the ground that it is 

 merely a matter of spatial and mechanical possibilities and, therefore, 

 has no morphological significance. But the presence of remnants of tlie 

 lost organs and their traces, as in Primula, is evidence of the loss. 



Reduction in the Androecium 



In reduction in the androecium, individual organs or entire whorls 

 may be lost. In related taxa, the inner whorl may be lost in some families, 

 as in the Iridaceae; the outer whorl in others, as in the Burmanniaceae 

 and Haemodoraceae. The Orchidaceae are an example of members lost 

 from both ancestral whorls. 



The origin and course of the vascular traces to the stamens in obdi- 

 plostemonous taxa support the theories of the loss of the outer androecial 

 whorl and of the union of the two whorls in those taxa that have only 

 one whorl but have double the number of members present in other 

 floral whorls. Obdiplostemony and the union of two stamen whorls 

 are steps in the shortening of the receptacle in specialization of the 

 flower by reduction. 



Ontogeny provides no evidence of value in the interpretation of obdi- 

 plostemony. Sequence in development among the various whorls of 

 organs in the flower is variable; it is probably less commonly acropetal 

 than otherwise. In Oxalis and Geranium, sequence in development of the 

 two whorls may be in either direction; in Commelina, the inner whorl 

 of stamens develops before the outer. 



Transformation of Fertile Stamens into Slaminodia. Reduction of the 

 androecium, whether spiral or whorled, by transformation of fertile 



