In this paper we describe an experimental study of relation for specific gravity of cane stalk with three components of cane stalk, that is, Ref Brix in milling juice, fiber content and pithiness ratio (piping in stalk) . It becomes clear to calculate correlation coefficients between four characters and to derive the regression equation involving four characters, (change) . We consider whether or not the experimental values agree well with the theoretical values of fiber content obtained by substituting the measured values of other three charatcers into the equation.
1) Simple and partial correlation coefficients between 4 characters used 17 varieties are shown as Table1. Simple correlations for specific gravity of cane stalk showed very high possitive values with fiber content and Ref Brix but showed no interaction with pithiness ratio. Partial correlation coefficients were calculated eliminating the influence of other two characters. Then, it was cleared that specific gravity of cane stalk was found a closely positive correlation, with fiber content (r=0.714) and Ref Brix (r=0.657) and high negative correlation with pithiness ratio (r=-0.656) .
2) The specific gravity (y) and 3 variable factors, fiber content (x₁), pithiness ratio (x₂), and Ref Brix (x₃) can be expressed by mean of the following equation (1) .
y=0.947+0.00941x₁-0.00525x₂+0.00166x₃……………………………… (1)
3) We rewrite the equation (1) as follow to express the fiber content (x₁) by other three factors, y, x₂, x₃.
x₁=-1000.692+106.318y+0.558x₂-0.177x₃………………………………… (2)
4) The theoretical values of fiber content used 67 seedling clones, obtained by substituting the measured values of y, x₂ and x₃ into the equation (2), agreed well with the experimental values and therefore showed the significant positive correlation by r=0.839.
5) We conclude from the experiment described above that fiber content of cane stalk may be estimated by measuring specific gravity of stalk, Ref Brix and pithiness ratio and using the equation without the traditional trouble treatment.

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