ALLIUM CEPA 107 



The inner cycle of perianth segments, and the inner stamens 

 which lie centrad to them, are differentiated following the forma- 

 tion of the outer whorls; and the first of the inner perianth seg- 

 ments with its stamen is formed between the oldest and second 

 oldest of the outer whorl. (Fig. 97, £.) The second and third 

 members of the inner cycles of perianth segments and stamens arise 

 in sequence in a clockwise direction, although in some instances 

 the direction is reversed. In most cases, the last segments to dif- 

 ferentiate are opposite the oldest but "somet mes segments of the 

 inner whorls lying both clockwise and counter-clockwise to the 

 oldest segments of the flower appear to arise simultaneously." 

 Although the inner stamens are differentiated later in ontogeny 

 than the outer ones, they are the first to shed their pollen. 



The carpellary primordia develop as the outer perianth segments 

 are beginning to overarch the stamens and appear as three cres- 

 centic outgrowths which arise on the flattened meristematic surface 

 alternate to the three inner stamens. (Fig. 98, A.') The young 

 carpels elongate, and owing to lateral and basipetal growth, their 

 inturned edges meet to form the three-loculed ovary of the pistil. 

 The style is differentiated by the apical growth of the three carpels; 

 and while the elongation of the style is taking place, the ovules 

 arise along placentae on the inner edges of the carpels, two being 

 formed in each locule. (Fig. 98, £-G.) Two integuments develop 

 which surround the nucellar tissue; and by the time of anthesis, 

 the ovule has become almost completely anatropous. 



Vascular Anatomy of the Flower. — At the upper limits of the 

 flower stalk, the vascular bundles of the outer cycle anastomose so 

 that they form a nearly continuous ring. Slightly higher, just 

 below the divergence of the bracts which constitute the spathe, 

 the entire vascular supply forms a complicated network of branch- 

 ing and anastomosing bundles from which the traces to the spathe 

 and to the pedicels of the individual flowers diverge. Each pedicel 

 has six vascular bundles arranged in two cycles as in the main 

 flower stalk of the umbel. At higher levels, the pedicel becomes 

 subtriangular, and the three outer bundles occupy positions centrad 

 from the angles, while the three inner bundles lie slightly within 

 the outer cycle and alternate to them. (Fig. 99, D, £.) 



Each outer bundle branches, one trace supplying a segment of 

 the outer perianth, the other the outer stamen which is subtended 

 by this perianth segment. The inner bundles supply the inner 



