ment with ammonium oxalate, or with hot dilute ammonium oxalate 

 and ammonia together, or with hot dilute hydrochloric acid, or with 

 hot water, failed to remove all ruthenium-red-staining substances. 

 Some of the latter reagents are said to be specific for pectins and 

 others for hemicelluloses (29). Considering these results together 

 with staining reactions it is concluded that pectins and hemicelluloses 

 occur in close association in cell walls and in the so-called pectic 

 structures. 



In material fixed after steaming, the hypodermis extended to a 

 greater depth, especially in Rome Beauty and Stayman apples (pi. 

 1, G, I). Cell walls of all varieties were less intensely and less uni- 

 formly stained (pis. 2, D, F; 3, B, D), the middle lamellae paler, and 

 the other pectic structures more prominent. Cell walls were also 

 usually swollen and often spongy in appearance. The middle lamellae 

 and cell walls thus both appeared weakened. The hypodermis of 

 Delicious apples retained greater staining capacity in both wall and 

 middle lamella than did the other varieties. Delicious samples showed 

 the least swelling of hypodermal cell walls, and Jonathan the most, 

 although the greatest thickness was attained in Stayman samples. 

 Except for the Jonathan variety (previously described as bruised 

 when received), no additional separation of hypodermal cells was 

 observed in steamed samples. 



In many slides made from steamed specimens, the spongy cell 

 walls when examined with polarized light showed a change of structure 

 here termed "flaky breakdown'' (pi. 4, B, C). Within the walls 

 there appeared highly birefringent bodies that were distinct in color 

 and other respects from the moderately birefringent cellulose of 

 unaltered cell walls. The bodies or "flakes" looked most like partially 

 gelatinized starch granules (pi. 4, F). They reacted negatively to 

 the iodine test for starch and to the tests used for pectins and pento- 

 sans. Their appearance in polarized light indicated the presence of 

 cellulose. They were not created in deparaffinized sections of un- 

 cooked apples by treatment with hot water or with fluids applied 

 for extracting pectins or hemicelluloses. The possibility is suggested 

 that the cellulose component of apple hypodermal cell walls can be 

 altered by steaming, a possibility also suggested by Simpson and 

 Halliday for the cellulose of carrot parenchyma (39), although from 

 different evidence. 



Flaky breakdown appeared to occur first in that part of the wall 

 nearest the middle lamella, but often the entire wall except for the 

 areas surrounding the pits was involved. It occurred sometimes 

 only at the edges of the sections (which circumstance points to the 

 possibility of an oxidative or enzymatic reaction as a part of the cause), 

 sometimes in the entire hypodermal segment of the sections. It 

 was seen in sections of some steamed-fixed samples of all varieties 

 but was not always present in any one variety. It was least common 

 and extensive in hypodermis from Delicious apples and most promi- 

 nent and extensive in hypodermis from Stayman and Golden Delicious 

 apples. A few birefringent bodies of apparently similar nature were 

 observed in the cell walls and middle lamellae of some stored samples 

 that had been fixed without steaming. 



The Cortex 



Apple cortex (fig. 2) is composed of large, thin-walled, loosely 

 arranged parenchyma cells with sparse vascular bundles scattered 



49&308 0^59 5 21 



