The process of formation of the abnormal bundles caused by 2,4-D was investigated, and obtained following results : 1. The intrafascicular cambium (IC) had high activity and larger meristematic region around phloem than normal ones (Photo. No. 2,No. 3) 2. Metaxylem (MX) was differentiated along the activated IC, therefore the MX located evcn in the upper position of metaphloem (MP). 3. The differentiation of protoxylem (PP) derived from IC was stimulated (Photo. No. 2) or limited (Photo. No. 4), and protoxylem lacuna developed irregular snapes. 4. MP was differentiated from the IC surrounding the phloem, and sieve tubes in the MP arranged centripetally. These results suggested that the intrafascicular cambium played the important roles on the process of formation of the abnormal bundles.