102 MORPHOLOGY OF THE ANGIOSPERMS 



monly no alternation (Fig. 48A). Under still another theory, that of 

 origin by division, which is supported by the frequent presence of epi- 

 petally, the new stamens were considered morphologically petals, formed 

 by tangential splitting of the petals, with the new inner organs trans- 

 formed into fertile appendages. (This theory arose from reading in the 

 wrong direction the common and readily interpreted series in the forma- 

 tion of staminodia and petals from stamens.) Evidence supporting the 

 corolline nature of the supposedly inserted whorl was seen in the stipule- 

 like appendages of the petals and stamens in some taxa. Strong objec- 

 tions were at first raised to the acceptance of the dedoublement theory, 

 even before abundant evidence showed that it has no support in ana- 

 tomical structure. 



Under the displacement theory, the new members in the stamen whorl 

 were considered to have reached their positions by differential growth, 

 displacement from an inner position. The displacement theory found 

 later support under the theory of carpel polymorphism, where "balloon- 

 ing," caused by the development of carpellary locules, was considered 

 to have pushed outward the antepetalous stamens, so that, in obdi- 

 plostemonous flowers, they stand farther out than the antesepalous 

 stamens. (Displacement of this sort would not be morphologically sig- 

 nificant, because it does not affect the level of origin of the stamen 

 traces. ) 



Involved in a discussion of possible intercalation of a whorl in the 

 androecium is a related aspect of major flower modification — the con- 

 densation of two stamen whorls by suppression of the internode between 

 them, with the insertion of the members of one whorl between those of 

 the other. Evidence of this step is seen in many eight- and ten-stamen 

 taxa in a not-quite-perfect whorl (the genus Acer is a good example) 

 and in the greater length or earlier development of alternate stamens. 

 The stamens of this double whorl may be perfectly aligned on one 

 level, but the members of one whorl usually stand a little outside those 

 of the other and their traces arise below those of the other whorl. This 

 condition gave support to the views of intercalation and to the long- 

 maintained displacement theory — that differential growth in the re- 

 ceptacle had brought the new whorl into union with the other. Growth 

 of this sort was believed even to move the inner whorl to a position out- 

 side the outer whorl and thus to bring about obdiplostemony. Evidence 

 of this was supposedly found in the course of the traces through the 

 cortex, but the position of trace origin was not noted. Union of two 

 whorls is well demonstrated in several families. In the papilionate 

 Leguminosae, the ten stamens may arise as two whorls but, in maturity, 

 form one; differential growth brings the whorls together, with resulting 



