POJUACE.E 



371 



are seen to arise from the concave sides of the torus. Follow- 

 ing the appearance of sepal primordia, appear petal primor- 

 dia, then those of stamens, and lastly those of the carpels. 

 The succession of floral cycles is acropetal, i.e., in order 

 from without to the inside. 



Fig. 155. — Diagram showing the development of apple. Dotted area repre- 

 sents pith. Not drawn to scale. (After Kraus, Oregon Agr. Exp. Sla.) 



The primordia of stamens appear in three cycles, those of 

 the outer usually being laid down first (Fig. 1 56). The carpel 

 primordia appear within the central portion of the cup-shaped 

 torus. There are .five of these surrounding a small central 

 cavity, which is formed by a lack of growth at the center of 

 the torus. Hence there is no common placenta, but each 

 carpel has its two separate placentas, which in "open-cored" 

 pomes may become closely connected. These facts will be 

 considered again in the account of fruit development. 



It is thus shown by the studies of Kraus that calyx lobes, 

 petals, stamens, and carpels are all outgrowths of the urn- 

 shaped receptacle. 



