104 MORPHOLOGY OF THE ANGIOSPERMS 



stamens into staminodia may occur in either outer or inner members 

 (Fig. 47A) or both; typically the outer members. Transformation of the 

 inner stamens seems to be the more primitive condition, as seen where 

 the petaloid staminodia form a prominent pseudocorolla above and 

 inside the androecium in Eupomatia (frontispiece). In other primitive 

 flowers — Degeneria, Hi7nantandra, Calycanthus, and some of the Moni- 

 miaceae, Nymphaeaceae, and Helobiales — staminodia are present both 

 above and below the stamens. If the upper position is the earlier one 

 in the evolution of the flower, as suggested by these primitive taxa, the 

 first "corolla" was above the stamens, a position which accompanies 

 pollination by beetles. 



Reduction in Stamen Number within Whorls. Aside from the reduction 

 of whorls in the androecium, loss of stamens within the whorl is a 

 prominent feature of specialization in many families. This loss accom- 

 panies zygomorphy and other adaptations to pollination methods. There 

 is often variety in reduction in stamen number within a family, as 

 from five to four and to two — Scrophulariaceae; even within a genus, 

 as in Polygonum, from nine or six to three and two. Reduction in 

 stamen number is in one whorl only or in both whorls and is of all 

 degrees; it ranges from suppression of a single stamen in the androecium 

 to suppression of all but one. Extreme reduction — to a single stamen — 

 is occasional, as in Euphorbia, Callitriche, Sarcandra, Najas, Casiiarina, 

 Hippuris, Lilaea, Zostera, Triglochin, Wolffia, Mangifera, most orchids. 

 Solitary stamens occur in flowers otherwise greatly reduced, chiefly 

 those of aquatic genera, of elaborate zygomorphic form, or of greatly 

 compacted inflorescences. In unisexual flowers, the solitary stamen has 

 often been claimed to be terminal on the receptacle and therefore 

 cauline in nature, but ontogeny and vascular structure of the entire 

 flower show such a stamen to be appendicular, a true microsporophyll 

 in a pseudoterminal position (Fig. 36). (In this respect, it is similar 

 to the pseudoterminal carpel.) Some so-called terminal stamens are 

 fused stamens; two or more connate sporophylls occupy a central posi- 

 tion in the flower — Salix (section Diandrae), Zannichellia, Typha. Evi- 

 dence that the solitary, apparently terminal, stamen is not morphologi- 

 cally terminal and cauline is seen in its ontogeny, for it arises off center; 

 in its form, it is not radially symmetrical, because two sporangia are 

 larger than the other two; and the anther is definitely dorsiventral. The 

 interpretation of solitary stamens and carpels as cauline involves the 

 acceptance of sporangium position in the angiosperms as both cauline 

 and appendicular. Indiscriminate sporangial position — cauline or foliar 

 — is found only in the lower plants, and the presence of both types in 

 the highest plants — even within a genus, as is seen under the Phyllo- 

 sporae-Stachyosporae theory — is morphologically inconsistent. 



