The reasons for the increase suggested in this paper, are as the following: (1) the parenchymous cells of pith ray turn into meristem strands and the meristem strands form new vascular bundles;

• 维管束数目不断增加是由于：(1)由髓射线薄壁细胞反分化产生分生组织束，分生组织束活动产生新的维管束；