Abstract: The isolation layer of the graft union is a changeable component. It is formed and thickened during the early stage (Fig. 6) and disrupted, thinned and even disappeared durmg tile later stage of development of the graft (Fig. 1, 2, 14). A number of vesicles, paramarat bodies (Fig. 3, 5, 8, 9, 11, 13, 19), multivesicular bodies (Fig. 4, 15, 16, 18, 20) and concentric membrane bodies (Fig. 7) are observed in callus 'beside the isolation layer during both stages of development based on transmission electron microscopy. The paramural body comprises invagination of plasmalemma containing numerous vesicles and/or tubules situated between the cell wall and the plasmalemma. The multivesicular body is a organelle about 0.5-μm in diameter with a single membrane surrounding several smaller single vesicles. It is possible that multivesicular body and/or single iesicles transverse the plasmalemma to produce paramural body. The figures show that the paramural bodies appear always beside the isolalion layer at the different stages of development of the graft union and the multivesicular bodies appear mostly near the region where plasmodesmata are secondarily formed between the stock and the scion (Fig. 15, 17, 20). This may reflect that paramural body and multivesi- cular body, as well as single vesicles, are capable of performing vesicular transport. The deposition and reabsorption of material of the isolation layer occur due to vesicular transport. All the above facts seem to indicate that paramural body, multivesicular body and single vesicles can be both endocytotic and exocytotic. The present study supports the theory of vesicular transport, and authors suggest that transcellular cytosis occurs not only through plasmodesmata but also through plasmalemma in oapoplast. The single vesicles, paramural bodies and multivesicular bodies take an active part in the transport process of symplast-apoplast-symplast.

Key words: Graft, Isolation layer, Paramural body, Multivesicular body