BETA VULGARIS 177 



each of which has in its axil a flower. The flower primordium forms 

 a small protuberance on which are soon differentiated five narrow 

 ridges, the beginnings of the sepals. Next there appears within this 

 circle a whorl of papillae, the stamen rudiments, each opposite a 

 calyx lobe. Finally, three more ridges develop at first separately; 

 but later joining to inclose a more or less compressed roundish cavity 

 in which a single ovule develops. 



"Once initiated, the primordia of the different floral parts develop 

 very rapidly. The young stamens become stalked early and attain 

 in cross section the characteristic quadrilocular form. The anther is 

 at first a homogeneous mass of tissue covered by an epidermis. As 

 soon as it becomes faintly 4-lobed in cross section the cells next to 

 the epidermis begin to elongate radially and divide periclinally, forming 

 two layers of narrow cells which by their size and staining reaction 

 appear distinctly set off from the central tissue which forms the arche- 

 sporium. These two layers of cells together with the epidermis 

 constitute the anther wall. The cells of the middle layer, in their 

 subsequent development, enlarge rapidly and finally develop thicken- 

 ing bands. This constitutes the endothecium and forms a continuous 

 mantle except in the region where the anther later dehisces. . . . 

 The cells remain small and as the anther enlarges they become stretched 

 tangentially, but they do not become obliterated before the endothecium 

 is fully developed and the pollen practically mature. 



"The ovule arises near the base of the carpels. It is seen first as a 

 slight protuberance which enlarges to form the nucellus. In its sub- 

 sequent development the young ovule becomes distinct from the surface 

 of the carpel by a stalklike base or funiculus. Very early there appears 

 at the base of the nucellus an annular outgrowth followed soon by a 

 second one of a similar nature. The first outgrowth develops into 

 the inner, the second into the outer integument. The young ovule 

 is straight, but with the appearance of the integuments it curves and 

 becomes campylotropous. Finally, the ovule twists about its own 

 funiculus and comes to lie horizontally in the cavity of the ovary." 



At the base of the receptacle, the vascular traces of the floral 

 organs form a short stele which is a somewhat irregular central 

 core rather than a dissected siphonostele. Five distinct groups of 

 vascular units diverge in the broader portion of the receptacle 

 occupying a peripheral position in the cortical zone, and the re- 

 mainder of the central core forms a single bundle which is con- 

 tinuous with the vascular supply to the ovule. (Fig. 138, A.^ 

 The vascular strands which diverge from the cortical region pass 

 out into the five calyx lobes, and each of these bundles later gives 

 off branches to form the lateral traces of the lobes. (Fig- 138, C'.) 

 The pistil, which consists normally of three undiverged carpels, 



