134 MORPHOLOGY OF THE ANGIOSPERMS 



have been considered possibly remnants of an ancestral telome system, 

 but they can, at least in large part, be interpreted as projections of the 

 connective, often reflexed and adnate to the body of the anther. The 

 Melastomaceae are an advanced family, and the projections suggest 

 modification of anther form related to uncommon methods of pollina- 

 tion, perhaps ornithophily. 



The "trunk" vascular supply to stamen fascicles is a compound 

 structure. That it consists of the connate traces of several to many 

 stamens is apparent from the presence in several primitive families — 

 Paeoniaceae, Dilieniaceae, Monimiaceae — of stages in the union of a 

 group of stamens (Fig. 46). "Branched stamens" are formed in this 

 way. Fascicled stamens have been considered branched stamens that 

 are perhaps homologous with the bennettitalian stamen, but the 

 branched microsporophyll of the Bennettitales has a single, simple trace. 



Ontogeny of the Stameh^ 



Ontogeny of the stamen is basically like that of sepal, petal, carpel, 

 and leaf; there is growth in length, width, and thickness. Early de- 

 velopment is by apical and marginal meristems (Fig. 58). Marginal 

 meristems are active for periods varying with the form of the filament 

 and anther. In winged filaments, they are well defined and long per- 

 sistent; in narrower filaments, they cease activity after periods varying 

 with the width of the filament; in terete filaments, they are absent. 

 Weak marginal meristems may be present in thick, subterete filaments. 

 In the connective, marginal growth is difficult to determine, because it 

 is weak and obscured by growth in thickness. Sufficient attention has 

 not, however, been given to details of the ontogeny of the connective 

 and filament. Critical ontogenetic studies should be made of anthers 

 with broad connectives and subterete filaments to obtain evidence in 

 support of the view that both margins are on one broad side of the 

 anther. 



The stamen primordium arises on the floral receptacle as a crescent- 

 shaped projection, where the filament is broad, or as a rounded pro- 

 jection, where the filament is terete or nearly so. The primordium 

 elongates rapidly and soon assumes roughly the form of the anther, 

 with some indication of its orientation and relation to the filament. 

 At this stage, the filament is represented merely by the base of the 

 primordium. Witli increase in size of the primordium, bulging areas 

 indicate the position of the sporangia. These regions develop rapidly 

 and the rest of the anther grows more slowly. Differential growth in the 

 connective and anther wall complete the development of mature 

 anther form. At this stage, differential growth is an important feature 



