POMACES 377 



Cross-section of Fruit. — In a median cross-section of the 

 apple fruit (Fig. 158), the relation of carpels and receptacle is 

 well made out. The five carpels radiate from the center. 

 Each carpel is composed of a parchment-like endocarp, 

 fleshy mesocarp, and fleshy exocarp. The pith of the re- 

 ceptacle, which is in reality stem, surrounds and unites 

 with the carpels; the pith is without vascular bundles. As a 

 rule, there are ten primary vascular bundles seen in the 

 median cross-section. They mark the limits of the pith, all 

 tissue outside of them being cortex of the receptacle. 



The tissues of the carpels and pith are very similar. How- 

 ever, the tissue of the carpels bears a network of very fine 

 vascular bundles, while that of pith is without such a network. 

 Many observers have wrongly considered all tissue from 

 parchment-like tissue, surrounding the seed cavities, out to 

 vascular ring, inclusive, as carpellary, whereas others have 

 considered only the parchment-like tissue as carpellary. 



The ten primary vascular bundles are related in their 

 development with the carpels, as is shown by the fact that 

 when six carpels occur there are twelve bundles instead of 

 ten, and when there are four carpels, eight bundles. 



Longitudinal Section of Fruit. — In longitudinal section 

 (Fig. 158), the flesh is seen to be separated into two parts by 

 a distinct fine, the "core Hne." The core line marks the 

 junction of pith and cortex of the receptacle. The primary 

 vascular bundles of the torus follow the core line, and 

 branches from them spread out into the cortex of the fruit. 

 Kraus has demonstrated that apple varieties show marked 

 variation in their internal structure, and that this structure 

 is distinctive for any given variety. 



External Characteristics. — These are very important in 

 technical descriptions of the apple. Form is of considerable 

 consequence. In judging form, the apple is held so as to 



