98 MORPHOLOGY OF THE ANGIOSPERMS 



in taxa show the clustering of numerous free stamens to form multi- 

 stamen fascicles, and reduction in number of fascicles and number of 

 stamens per fascicle. In the Dilleniaceae, Wormia, Dillenia, and Hib- 

 bertia form an obvious series in evolutionaiy specialization in flower 

 structure and in habit, from trees to small shrubs and vines. In Dillenia, 

 where there is no external grouping among the many spiral stamens, 

 tnmk vascular supplies bind clusters of stamens together anatomically. 

 In the first two genera, the stamens are free; in Hibbertia, the stamens 

 are in fascicles. Hibbertia is a large genus of small shrubs and woody 

 vines, with high specialization in flower structure — zygomorphy of 

 corolla and androecium in its most advanced species. The zygomorphy 

 is expressed most strongly in the androecium. In the Hypericaceae, 

 Ascijron and other genera have numerous free stamens; within the 

 genus Hypericum, there is a series from free stamens to the fasciculate 

 condition, with reduction from five to three fascicles, and in stamen 

 number per fascicle from many to three. 



Anatomical stiucture supports the interpretation of some supposedly 

 simple stamens and nectaries as end products of the reduction of fasci- 

 cles. The androecium in the Lauraceae and in Parnassia shows evidence 

 — both from comparison of external form and of vascular structure — of 

 strong reduction. Some of the stamens and nectaries (in the Lauraceae, 

 modified stamens) have lateral or basal appendages (Fig. 45). Ana- 

 tomically, these appendages represent individual stamens connate in a 

 fascicle with a fertile stamen or with other sterile members of an 

 original fascicle. In Sassafras and Umbellularia (Fig. 45A to C), the 

 nectariferous basal lobes of stamens have independent vascular traces, 

 two extending from the receptacular stele into tlie lateral structures, 

 the other to the anther; the typical fertile stamen has only one trace. In 

 Benzoin, the glandular stamen has three traces, one extending into each 

 lobe. Each stamen in Laurus has three vascular bundles, two supplying 

 the lateral lobes. Each of the several lobes of the staminodium of 

 Varruissia has an independent trace; the unlobed stamen has several 

 traces arranged in the filament in a loose cluster. The stamen and the 

 staminodium (nectary) of this genus are homologous structures, repre- 

 senting greatly reduced stamen fascicles with connate members. (The 

 presence of the vascular bundles of several connate stamens within the 

 "filament" of die typical stamen is an excellent example of the per- 

 sistence of vascular structure after external form has been lost.) The 

 existence of fasciculate stamens in these taxa is of phylogenetic im- 

 portance. It supports the view — maintained by cytological evidence — 

 that Parnassia does not belong in the Saxifragaceae; it aids in determin- 

 ing the relatives of the Lauraceae (Chap. 11). 



Though the existence of "trunk" vascular supplies for fascicles would. 



