xo6 THE STRUCTURE OF ECONOMIC PLANTS 



stamen, which it subtends, becomes evident. In most instances, 

 the two appear to be differentiated simultaneously from a common 

 meristematic region, the outer portion of the primordium forming 



opl 

 J 



Fig. 97. A, a. slightly older stage in floral development than in preceding figure, /; fp, 

 flower primordia ; B, side view of three flower primordia ; C, top view of a young flower 

 showing counter-clockwise diff'erentiation of outer perianth lobes, opl, and outer whorl of 

 stamens. The youngest primordium VI will appear opposite the oldest perianth segment I; 

 D, longisection of a portion of inflorescence at about the time that floral organs of the oldest 

 flowers are beginning to diff'erentiate ; E, top view of a young flower showing outer whorls 

 of perianth and stamens differentiated. The inner whorls are just beginning to differentiate. 

 Roman numerals indicate sequence of origin of different segments ; F, side view of flower 

 slightly younger than one shown in E; G, top view of young flower in which primordia of all 

 perianth segments have been differentiated : ipl, inner perianth lobe ; ist, inner stamen ; ost, 

 outer stamen. (After Jones and Emsweller, Hilgardia.^ 



the perianth segment and the inner part, one of the outer stamens. 

 The outer perianth segments arise in a counter-clockwise direction, 

 and the stamens follow the same order. (Fig. 97, C.) 



