PART II.— MICHOSCOPICAL EXAMINATIONS OF FRUITS AND 



FRUIT PRODUCTS. 



By Burton J. Howard. 



The close structural similarity of many of the fruits used in canning 

 makes the problem of the identification of the constituents by no means 

 easy. Apple pulp, which is used as a filler in many fruit products, is 

 so devoid of characteristic structure that any method giving hints as 

 to its presence is of value. It is a well-known fact that starch is 

 usually present in most fruits during some periods of growth, but 

 that in many it more or less completely disappears when the fruit 

 is ripe. AVith this in mind, some examinations were made of apples, 

 pears, peaches, quinces, grapes, raspberries (red and black), strawber- 

 ries, and tomatoes, in various stages of ripening. Apples more than 

 any other fruit are used in an immature state, and starch can often 

 be detected in fruit products composed wholly or in part of apples. 

 Concerning the morphological features of apple starch it may be said 

 that it consists of both simple and compound grains. The simple 

 grains are globular in form, and according to Browne '"" are about 9 

 microns in size. This size, however, we have found to vary greatly, 

 since in maturing the grains are converted into sugar and during this 

 period decrease in size. In one specimen the average size was found 

 to be 9 (3.5 to 14) microns, while in another it was 11.8 (7 to 17.5) 

 microns. This fact of change in size was strikingly shown in the case 

 of two Kieft'er pears. In one which was nearly ripe the average was 

 4: (1.5 to 5) microns, while in a green specimen the size was 13 (3 to 29) 

 microns. The compound grains, which are very abundant in green 

 fruit, are composed of 2 to 5 grains attached together, giving a clus- 

 tered or tetrahedral effect. Such grains are seldom seen in samples 

 of apple starch obtained by grating and sedimentation, since they 

 are easily broken up into truncated simple grains in the process of 

 grating. The grains are marked by a stellate or linear fissure or 

 depression and some with a good light show faintly concentric rings. 

 The grains are active toward polarized light, and show colors with the 

 selenite plate. As the apple ripens, starch begins to disappear near 

 the center of the fruit, and later at the periphery. The last traces are 

 to be found in the cells adjacent to the fibrovascular bundles. Fully 

 ripe apples contain no starch whatever except in bruised portions. 



^Peniia. Dept. of Agric, Bull. 58. 



103 



