black: inflorescence and fruit of PYRUS MALUS 539 



The apple fruit is the result of a combination of the growth of 

 the inferior ovaries and the torus of the receptacle. The identi- 

 fication of the various parts of a mature fruit is made by com- 

 parison with the origin and development of these parts in the 

 flower and immature fruit. It has been shown that the sepals, 

 petals, stamens, and pistils arise successively from the meriste- 

 matic surface of the concave torus. The great growth of the 

 torus and underlying parenchyma elevates the circles of sepals, 

 petals, and stamens in succession, so that they gradually assume a 

 position above the pistils — plate 35, figures 3 to 7; plate 36, 

 FIGURES I and 2. The pistils thus become inferior. A com- 

 parison of the developing flower and the immature fruit (plate 37, 

 FIGURES I and 2; plate 38, figures i to 6; plate 39, figures 

 I to 5) furnishes the basis for the following description of the 

 formation of the fruit. The five pistils in the flower (plate 35, 

 FIGURES 3 to 7) arise from the embryonic tissue of the torus 

 around the apex of the axis which is not entirely used up. Each 

 pistil is united to its neighbor by the tissue of the torus, thus 

 forming a continuous ring, except that part becoming the style. 

 Sections cut near the apex of the fruit show the styles still united 

 peripherally, but distinct centrally, with the grooves^ leading to 

 the ovarian cavities (plate 39, figure 3). Sections cut at a higher 

 point show the five now distinct styles with their grooves centrally 

 faced (plate 38, figure 6). 



The parenchymatous tissue just beneath the meristematic end 

 of the axis and the organs produced upon it becomes the pith. As 

 the torus becomes more concave the pith area also conforms to 

 this shape. This has been shown in a diagrammatic way by 

 Kraus. The developing pistils thus become enveloped by the 

 increasing torus with which they have always remained united 

 (plate 36, FIGURES I and 2; plate 37, FIGURES I and 2; plate 38, 

 figures 4 and 5). That part of the section properly pistil is 

 clearly distinct from that which is torus as shown by the finer cells 

 and by the network of small vascular bundles outlining each carpel 

 as found in figures 4 and 5, plate 38. 



Growth proceeds rapidly in the pistil and torus, following the 



^ In the apple the gynoecium is more sensitive to frost than the other floral organs. 

 This greater susceptibility to cold has frequently been attributed to the sensitiveness 

 of these parts, whereas it seems more reasonable to explain it as due to the exposure 

 occasioned by the structure of the pistils. 



