EXAMINATIONS OF APPLE STAKCH. 93 



The appearance of more intercellular air in the tissues and the con- 

 sequent lessening of the specific gravity of the fruit are also correlated 

 with the ;; mealiness" of the fruit. It is a matter of common knowl- 

 edge that certain apples -when ripe are more "mealy" than others, and 

 that in some varieties this quality increases greatly just before decay. 

 ! I' a small piece of a mealy apple is carefully crushed and then exam- 

 ined under the microscope, it is found that the cells, for the most part, 

 have not been ruptured, but have simply been separated from each 

 other. This has been made possible by the softening of the middle 

 lamella} of the cell walls, which occurs in the last stages of ripening. 

 The middle lamella becomes so very weak that under a slight shearing 

 force it gives way, thus allowing the adjacent cells to separate without 

 rupturing their walls. 



In the earlier stages of the ripening of the fruit a very different 

 condition exists, because then the middle lamellae are strong, and the 

 cells rupture instead of splitting apart when subjected to pressure. 

 The softening of the middle lamella may also be artificially accom- 

 plished by boiling. A striking illustration of this is found in the 

 process of making apple butter, in which boiling is continued until the 

 cells fall apart when stirred. The readiness with which this occurs 

 varies with the different varieties and the decree of ripeness attained. 

 This difference in the behavior of the middle lamella in the readiness 

 with which it is dissolved by heat the housewife recognizes under the 

 common expression of difference of " cooking qualities," and she selects 

 apples with regard to this property as well as that of flavor. The 

 softening of the middle lamella, whatever its cause, serves, in part at 

 least, .to explain the difference in the mealy texture of apples which 

 may have the same percentage of juice, since in one case the process of 

 mastication does not accomplish the rupturing of the cells, which, like 

 little bags or capsules, retain the juice. Freezing also appears to 

 have a similar softening effect upon the lamella, inasmuch as apples 

 which have been frozen have a decidedly mealy texture and soft 

 consistency. 



In normal ripening the softening of the middle lamella results in a 

 slight change in the contour of the cell wall, so that the cell is more 

 regular in outline. The intercellular space is increased, and, as there 

 is usually but little liquid to fill the cavity, the amount of intercellular 

 air is increased. When viewed under the microscope, the presence of 

 air in some varieties is very noticeable indeed when nearly ripe, while 

 in the greener condition it is but little in evidence. 



An experiment was conducted to show the difference in the readi- 

 ness of disintegration (dependent on the softening of the middle 

 lamella in the same fruits) under different conditions of storage. 

 Cubes of as nearly the same size as possible were cut from two sam- 

 ples and placed in test tubes with a given amount of water. One set 



