Slides from Delicious and Stayman apples were treated with 

 cuprammonium hydroxide to remove cellulose and were stained with 

 iodine. After this treatment the outer zone of the cuticle contained 

 numerous horizontal brown-lined tubules not seen in sections receiving 

 other treatments. 



In polarized light the cuticle was moderately to weakly birefringent 

 (doubly refractive). Birefringence was usually strongest in the inner 

 zone and weak or lacking in the outer zone. Variations in this respect 

 did not appear to be closely related to variety, maturity, storage 

 conditions, or steaming. 



The hypodermis. — The hypodermis (fig. 2) is a region from 4 to 10 

 cells thick just inside the epidermis. The cells are larger than those of 

 the epidermis and gradually increase in size toward the cortex. The 

 walls are thickened and contain only irregular deposits of cutin. The 

 walls become thinner toward the cortex. The apple varieties studied 

 fell into two groups with regard to depth of hypodermis, size of its 

 cells, and thickness of its cell walls (table 3) . In Stayman and Rome 

 Beauty apples the hypodermis extended to the greatest depth, and its 

 cells were the largest and had the thickest walls (pis. 1, F, H; 3, A, C). 

 The hypodermis of Golden Delicious (pi. 2, C), Jonathan (pis. 1, D; 

 2, E), and Delicious apples (pis. 1, A; 2, A) was shallow and consisted 

 of smaller, less thick-walled cells. 



Structures that stained with ruthenium red were often prominent 

 in the hypodermis. They were middle lamella, extracellular sheath 

 and nodules, intercellular junctural masses, and circles or crescents 

 (bright-colored areas surrounding pits) (44)- They were least 

 prominent where cell walls as a whole were intensely stained and most 

 prominent (by contrast) where lightly stained. Structures staining 

 with ruthenium red are referred to as "pectic structures, " while keep- 

 ing in mind the likelihood that they contain other substances also. 

 Among the unstored samples, the hypodermis of Golden Delicious 

 and Stayman apples had the most prominent pectic structures. 

 In the hypodermis of Delicious unstored samples the overall stain 

 was most intense and the pectic structures were not evident; after 

 7 months' storage they were evident though not prominent. Rome 

 Beauty and Jonathan apples had pectic structures of medium promi- 

 nence at first; after storage their pectic structures were more promi- 

 nent, and after 7 months they resembled more nearly those of Golden 

 Delicious and Stayman. These same structures were colored brown 

 by diphenylene diamine acetate (pis. 3, 4), which stains pentosans 

 as well as cutin (14)- Nodules and junctural masses also sometimes 

 appeared bright red when stained with Congo red and Sudan IV. 



When examined in sections with polarized light, the hypodermal 

 walls were moderately and uniformly birefringent and faintly 

 laminate (pi. 4, A) . In surface view they were less strongly birefringent 

 and, where not interrupted by pits, often exhibited a faint pattern of 

 crisscross striations resembling threads in a woven cloth. 



When cellulose tests were applied to deparafhnized sections, cell 

 walls were blue; in some a delicate brown film was seen in the region 

 of the extracellular sheath (pi. 4, A). When sections were treated 

 with cuprammonium hydroxide, the cellulose was removed, leaving a 

 cellular framework that stained with ruthenium red. Treatment of 

 sections of raw-fixed or steamed-fixed material with hot dilute sodium 

 hydroxide removed all ruthenium-red-staining substances and left 

 a cellular framework which gave a strong cellulose reaction. Treat- 



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