applications of complete fertilizers did not change significantly the concen- 
tration of chlorophyll in the skin of fruit but concentration of total caro- 
tenoids was significantly increased with such fertilization. 
Desrosier, Billerbeck, and Tukey (16) developed a reflectometer using 
appropriate filter-photocell-light source combinations and a sample rotator, 
which showed a good relationship between external color measurement and the 
U. S. grades for apples. The so-called Purdue color ratio meter viewed the 
entire surface of the apple except for small areas at the stem and calyx ends. 
Francis (21) on the other hand used a color and color difference meter, 
long used in the paint and varnish field of color evaluation, to study skin 
color in apple varieties. Tests with the Photovolt instrument were not as 
conclusive as the Hunter Color and Color Difference Meter (CDM). His results 
indicated fair_to good correlation of visual ratings of fruit with Hunter Rd, 
a, b, and tan ~ a/b ratio values, A sample rotator used with the colorimeter 
was considered to integrate the variable colors over the surface of the apple 
sample, but such measurement is open to question due to the constant changing 
of geometry in the color measuring system as the fruit revolves over the ex- 
posure head of the instrument. 
Wiley and Thompson (90) used the Hunter CDM to relate raw flesh color 
to processed apple slices. They concluded that approximately 45 percent of 
the overall grade for finished product was accounted for by color; factors of 
wholeness and firmness (47.5%) and flavor (7.5%) accounted for the remainder 
of the grade. 
Carrying reflectance measurement a step further brought the development 
of the automatic apple sorter which has been used in the Pacific Northwest. 
Larsen (38) reports an objective color sorting system whereby fruit surface is 
scanned by eight lights, the light from which is reflected upward to be charac- 
terized by photoelectric cells as to extent of redness or lack of redness, The 
instrument sorts intact fruit into extra fancy, fancy, and No. 1 grade. The 
rapid rate of speed (1260 fruit per minute) enables handling of large quantities 
of fruit which would require many people to sort who would be subject to fatigue 
and variation in color memory. With change of filters the instrument will sort 
red and yellow apple varieties equally well. 
Boynton, Compton, and Fisher (4) showed that leaf chlorophyll level 2.0 
to 2.2 mg/65 em? surface (one side) corresponded to color standard #4 specified 
by the New York Agricultural Experiment Station. Such a color designation was 
associated with a nitrogen status of spring fertilized trees high enough for 
maximum yield. A greater chlorophyll content might indicate nitrogen status 
above that necessary for maximum yield with unnecessary reduction in fruit 
color at harvest. 
Shear and Horsfall (71) also used the New York color standards for leaf 
chlorophyll and suggested that for standard #1 the percentage nitrogen level be 
raised from 1,5 to 1.73 color standard #2 from 1.7 to 2.03; color standard #3 
from 1.9 to 2.33 color standard #4 from 2.1 to 2.73 and color standard #5 from 
2.3 to 3.1. These standards were for York and Stayman apples. 
Clijsters, Wolvertz, and Sironval (7) suggest a procedure for the ex- 
traction of chlorophyll as a guide to the harvest of Jonathan apples to avoid 
rot in storage. They found that fruit that contained less than 30 micrograms 
chlorophyll per 10 cm? of skin would not store well regardless of red pigment 
development. 
