4, Scalpel or similar sharp instrument. 
5. Small bottles or vials. 
6. Acetone or petroleum ether. (CAUTION: Flammable solvents.) 
Procedure: 
1, Divide the green-mature fruits into two uniform lots, A and B. 
2. Ripen fruits of lot A for 10 to 14 days with illumination of daily dura- 
tion of 1 hour, Longer periods may be given but are not necessary. 
3. Ripen fruits of lot B 10 to 14 days in total darkness, taking care not to 
remove from darkness until ripe. These should ripen simultaneously 
with their lighted counterpart. 
4, When the fruits are ripe, remove uniformly shaped and size sections 
from a typical fruit from each lot, being careful to keep the sections 
separate and properly identified as to treatment. Immerse each section 
in boiling water for 1 minute and cool immediately by immersion in 
cold water; thus the skin is readily removed from the tomato flesh. 
Scrape the adhering tissue from the skin with the scalpel as carefully 
and completely as possible. Place each scraped skin section in one of 
the small containers containing acetone or petroleum ether solvent and 
leach the skins with several washings (keeping the sections immersed) 
over a period of at least several hours. 
Observations: 
The fruits ripened in the dark will be pink; those ripened in the light will 
be orange-red. CAUTION: Fruits will ripen faster at temperatures higher 
than 70° F., but at those higher temperatures the red pigment in the flesh 
does not develop well and gives the fruit an off-color appearance. The skin 
of fruits ripened in the dark will be colorless; the skin of those ripened in 
the light will have a yellow color even after prolonged leaching with the 
solvent. The insoluble light-induced yellow pigment left in the tomato fruit 
cuticle (skin) has not yet been identified. The presence or absence of the 
light-controlled pigment in the skins makes them either yellow or trans- 
parent. When the yellow skin is superimposed over the red, the fruit has 
an orange-red appearance, the typical coloration of summer field-ripened 
tomato fruits. The combination of red fleshanda transparent skin produces 
a fruit that is pink. The pink color is characteristic of fruits commercially 
available in the North in midwinter that have been artifically ripened in 
darkness by vegetable wholesale distributors. If fruits ripened in the dark 
have yellow-tinted skins, the leaching process was not complete or the 
fruits were too mature and were already producing the light-responsive 
pigment at the time the fruits were placed in the dark, Light starts to act 
as soon as the fruits mature. 
Supplementary Reading: 
Piringer, A. A., and Heinze, P. H. Effect of light on the formation of pig- 
ment in the tomato fruit cuticle. Plant Physiol. 29: 467-472. 1954. 
U.S. Agricultural Research Service. Light link in tomato. U.S. Dept. Agr., 
Agr Rese 2:0. 1954. 
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