The F3 of the cross tangerine x Palla Oro (Golden ball) shows that F2 tangerines are of two kinds: homozygous r^+^r^+^tt like the parental tangerine and heterozygous r^+^rtt segregating in 3:1 tangerine and yellow tangerine.
So the yellow tangerine is definitely shown to have the phenotype rr tt. The genetic results and also the biochemical researches on the maturation of fruits at different temperatures, concur in demonstrating that the gene t. in homozygous condition, always effects the synthesis of prolycopen, even without participation of the r^+ gene.
In absence of r^+ however, the quantity of lycopen synthesized is scanty, as if the r^+ gene could determine, according to the allele present, the quartity of the precursor substance wherefrom the two stereoisomers could be derived through specific enzymes each one finding optimal condition at a specific thermic level.
In the F3 of this cross occur phenotypes with pale yellow tangerine with rose endocarp. They have a carotene content higher than in the parental breeds and little quantities of prolyconene and more or less relevant traces of lycopene. A possible interpretation is the existence of a new genic system responsible for the early synthesis of the pigment (whatever it is, lycopen or Z-carotene or both of them mixed) chiefly located in this part of the fruit. A plan of researches is designed apt to solve this new problem.