The main purpuse of this study is to disscus mechanically the relation between the angle of fibrillar orientation and the longitudinal strain for the assumed model of tracheid which is compounded by two different thick cylinders consisted of steel helical spring, and to analyse the cause of small modulus of longitudinal elasticity in compression wood. If the head of model ( Fig. 1) is uniformly compressed without buckling to the axial direction by force P below elastic limit the pressure q per unit area of contact surface of compound cylinders develops, then the longitudinal strain of model εz and the tangential strain εt at contact circumferential surface shall be expressed by the following equation. [the equation is omitted] then q will be determined from the two conditions that εz1=εz0 and εt1=εt0. For the calculation of E and m, I assume the helical spring which the total length of steel wire l is satisfied with the next conditions; l=2πRn/cosα=h/sinα and use the following ezuations; [omitted] An example of results obtainable by these equations is shown in Table 2. From this table it is evident that as α in the inside cylinder decreases εz increases, consequently the modulus of longitudinal elasticity of the model decreases. From the above-mentioned results one of the causes that the modulus of longitudinal elasticity of compression wood is ever very small to comparison with normal wood may be existed in the lower fibrillar slope in the center layer of the secondary wall of compression wood tracheid.