ORGANIZED DEVELOPMENT IN PLANTS
67
2 hr, the region of future primary vascular tissue showed an increased
peroxidase activity which he related to the capacity of this tissue to
oxidize lignin precursors potentially of importance in xylem maturation.
Other tissues also showed increased peroxidase activity dependent on
auxin concentration and stage of maturity. A direct relation between
these events and xylem maturation remains to be explored.
C. Vascular Tissue Formation in Tissue Cultures
Tissue culture studies have contributed considerably to our knowledge
of the hormonal control of vascular tissue differentiation. This evidence
also has been reviewed in detail (Gautheret, 1957, 1959). In general,
plant tissue cultures, either derived from shoot or from root tissues, when
cultured on a nutrient medium containing auxin, show continued cell
proliferation and random internal differentiation of xylem and, although
less frequently reported, phloem elements.
Ball (1955) studied the effects of different kinds of sugars on the internal differentiation of nests of tracheary cells in callus tissue of Sequoia.
He found that there were considerable differences in the amounts of
vascular tissue differentiation when the tissues were grown on different
sugars. Tissues grown on fructose showed the least tracheid formation,
galactose produced the most, and sucrose was intermediate in its effect.
No interpretation of this response was attempted.
Kuroda (1960) reported a special case of vascular tissue differentiation
when two tissue pieces of carrot root, each containing the vascular
cambium region, were placed atop one another but with the cambial
regions not superimposed. At the union of the two tissue pieces, a newly
regenerated cambial zone developed, and then new tracheids differentiated and followed the same course as the regenerated cambial region.
Such differentiation was under the influence of cell-division stimuli
produced within the tissues themselves.
Camus (1949) showed that, when one grafted a bud into a tissue fragment of endive root grown in culture, cell divisions occurred in the tissues
below the bud and vascular tissues differentiated basipetally from the
newly divided cells. Induction could take place across a permeable membrane. Wetmore and Sorokin (1955) extended these observations to stem
callus tissues of Syringa. They found that if, instead of grafting a bud
into the cultured tissue, one simply placed a drop of agar containing
NAA and sucrose in a wedge cut into the top of the callus, one could
induce vascular tissue differentiation in the tissue below the site of
auxin application. The combined sugar and auxin induced the formation
by localized cell divisions of small masses or nests of cells which dif-
67
2 hr, the region of future primary vascular tissue showed an increased
peroxidase activity which he related to the capacity of this tissue to
oxidize lignin precursors potentially of importance in xylem maturation.
Other tissues also showed increased peroxidase activity dependent on
auxin concentration and stage of maturity. A direct relation between
these events and xylem maturation remains to be explored.
C. Vascular Tissue Formation in Tissue Cultures
Tissue culture studies have contributed considerably to our knowledge
of the hormonal control of vascular tissue differentiation. This evidence
also has been reviewed in detail (Gautheret, 1957, 1959). In general,
plant tissue cultures, either derived from shoot or from root tissues, when
cultured on a nutrient medium containing auxin, show continued cell
proliferation and random internal differentiation of xylem and, although
less frequently reported, phloem elements.
Ball (1955) studied the effects of different kinds of sugars on the internal differentiation of nests of tracheary cells in callus tissue of Sequoia.
He found that there were considerable differences in the amounts of
vascular tissue differentiation when the tissues were grown on different
sugars. Tissues grown on fructose showed the least tracheid formation,
galactose produced the most, and sucrose was intermediate in its effect.
No interpretation of this response was attempted.
Kuroda (1960) reported a special case of vascular tissue differentiation
when two tissue pieces of carrot root, each containing the vascular
cambium region, were placed atop one another but with the cambial
regions not superimposed. At the union of the two tissue pieces, a newly
regenerated cambial zone developed, and then new tracheids differentiated and followed the same course as the regenerated cambial region.
Such differentiation was under the influence of cell-division stimuli
produced within the tissues themselves.
Camus (1949) showed that, when one grafted a bud into a tissue fragment of endive root grown in culture, cell divisions occurred in the tissues
below the bud and vascular tissues differentiated basipetally from the
newly divided cells. Induction could take place across a permeable membrane. Wetmore and Sorokin (1955) extended these observations to stem
callus tissues of Syringa. They found that if, instead of grafting a bud
into the cultured tissue, one simply placed a drop of agar containing
NAA and sucrose in a wedge cut into the top of the callus, one could
induce vascular tissue differentiation in the tissue below the site of
auxin application. The combined sugar and auxin induced the formation
by localized cell divisions of small masses or nests of cells which dif-