... 1971 ). In thisway, the direction of growth of the mainroot axes is maintained, both outwards,away from the tree, and in the verticalplane. The way in which the direction ... related to the angle of initiation, and thus to the angle of the primary xylem line (Fig. 2).Sinkers and side roots were predomi-nantly initiated in a downward and in a ... lateralsare initiated in vertical files related to the position of the vascular strands in the taproot. The taproot of Q. robur, forexample, has 4-5 strands (Champagnatet al.,...