Agriculture Reference
In-Depth Information
formed (Figure 14.3(C)), cells of callus tissue have systemless arrangement. However,
in the zone of newly formed leading elements and while moving to them, they are
located in regular elongated rows.
As a result, the fi rst elements of a leading system—tracheides—are formed from
meristem spots in separate areas of callus, and near them closer to primary bark—
sieve-shaped tubes. Similar tracheid-shaped cells belong to a widely spread type of
water-carrying elements, called hydroxides. Callus hydroxides differ from water-
carrying anatomical elements of other types: cell nuclei are kept longer in them; cell
thickening lignifi es though [17].
As Figure 14.3 shows, the process of changing callus cells into hydrocides, which
starts deep in the wedge, spreads and gradually reaches the areas that are closer to cal-
lus periphery, forming ramifi cation in all directions. Finally, not far from the periphery
each band, which consists of hydorcides and accompanying sieve-shaped tubes, has
accumulated hydrocides at the end; they are alternated with the cells that have thick
cytoplasmatic content that resembles meristem. The accumulation of hydrocides and
meristem cells looks like wedge-shaped nodes (Figure 14.3(C)).
In Figure 14.3, one can see that a protective tissue in the place of grafting was
turned back toward the bud. This proves that out of the two callus layers where differ-
entiation processes take place, the one that belongs to rootstock is stronger and cell dif-
ferentiation occurs more energetically there. The process under consideration, which
identifi es the contact of vascular systems, is the most crucial for successful grafting.
However, the width of hydrocide band, which performs water supply, is rather small
and ranges from 0.3 mm in the place, where callus cells of the rootstock and grafted
bud join, to 3 mm in the area of intensive bud growth.
This narrow hydrocide band is located near a grafting periphery; that is why ex-
tended constriction of the area with polymer materials used for grafting can have a
negative effect on root stock water supply.
Among the well-known methods of vegetative propagation of apple trees, grafting
(or bud grafting) and improved copulation are of great practical importance. The lat-
ter is used for fast growing of young apple trees [18]. Studying the grafting place of
one-year-old apple trees, using the above-mentioned methods, on longitudinal radial
cut, showed (Figure 14.4(A)) that the use of improved copulation method enabled the
joining process of xylem and phloem elements.
Looking at a cross-section projection of the grafting place, one can see a continu-
ous ring-shaped system of leading elements, which ensures both a reliable joint of
scion and rootstock, and proper movement of nutrition elements and water. A protec-
tive tissue, formed in the joint places of grafting elements, is quite small; it is located
in the central part of the young tree and belongs to core elements.
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