64
JOHN G. TORREY
reference to thiamine and ascorbic acid (Running, 1950), boron (Skok,
1941-1942), wound substances in regenerating cambia (Brown, 1937),
and other unknown factors (Warren Wilson and Warren Wilson, 1961),
some of which may act in hormonal fashion. It is interesting to note that
under certain circumstances gibberellins have been shown to stimulate
secondary vascular tissue formation; in these cases also there was at
first the initiation of cell divisions followed by differentiation of vascular
tissues. Bradley and Crane (1957) reported such a response in spur shoots
of apricot sprayed with gibberellic acid (GA). Following GA treatment,
they found a marked increase in cell divisions in the vascular cambium
and an approximately fivefold increase in secondary xylem formation,
with no significant effect on phloem differentiation. Wareing (1958) noted
that combined treatments with IAA and GA produced a marked increase
in cambial divisions and xylem formation in debudded stems of Acer
and certain other woody species tested. GA treatment alone led to cell
divisions in the cambium, but poor secondary wall formation. He concluded that auxin was particularly active in stimulating xylem differentiation and that the interaction of GA and IAA together resulted in
nearly normal secondary xylem development. These experiments have
been extended in more recent work (Wareing et al., 1964).
Sorokin et al. (1962) made an anatomical study of the effects of kinetin in the presence or absence of the auxins IAA or 2,4-D on isolated
segments of etiolated pea epicotyl segments. The auxins alone produced a
marked stimulation of vascular cambial divisions with the formation of
considerable, but somewhat abnormal, secondary xylem. Kinetin treatment, in the presence or absence of added auxin, resulted in even more
marked cambial proliferation, with almost completely normal secondary
xylem development.
Initiation of secondary vascular tissue in roots appears also to be
under hormonal control, especially hormones moving from the aboveground portions of the plant into the root. The subject has been reviewed by Torrey (1963), and experimental evidence concerning the
essential role of auxin in cambium formation in isolated pea roots grown
in culture was given. Since isolated roots in culture do not usually form
any secondary tissues, the demonstration that excised roots can be induced routinely to form vascular cambium and extensive secondary
vascular tissues by providing them sugar and hormones via the cut
root base opens up the study of this aspect of hormonal control of
organization in roots. In roots of pea Pisum sativum, IAA at 10~
5 M
provided together with 8% sucrose via the root base led to cambium
initiation which progressed with time toward the root tip.
Loomis and Torrey (1964) applied the same technique to excised roots
JOHN G. TORREY
reference to thiamine and ascorbic acid (Running, 1950), boron (Skok,
1941-1942), wound substances in regenerating cambia (Brown, 1937),
and other unknown factors (Warren Wilson and Warren Wilson, 1961),
some of which may act in hormonal fashion. It is interesting to note that
under certain circumstances gibberellins have been shown to stimulate
secondary vascular tissue formation; in these cases also there was at
first the initiation of cell divisions followed by differentiation of vascular
tissues. Bradley and Crane (1957) reported such a response in spur shoots
of apricot sprayed with gibberellic acid (GA). Following GA treatment,
they found a marked increase in cell divisions in the vascular cambium
and an approximately fivefold increase in secondary xylem formation,
with no significant effect on phloem differentiation. Wareing (1958) noted
that combined treatments with IAA and GA produced a marked increase
in cambial divisions and xylem formation in debudded stems of Acer
and certain other woody species tested. GA treatment alone led to cell
divisions in the cambium, but poor secondary wall formation. He concluded that auxin was particularly active in stimulating xylem differentiation and that the interaction of GA and IAA together resulted in
nearly normal secondary xylem development. These experiments have
been extended in more recent work (Wareing et al., 1964).
Sorokin et al. (1962) made an anatomical study of the effects of kinetin in the presence or absence of the auxins IAA or 2,4-D on isolated
segments of etiolated pea epicotyl segments. The auxins alone produced a
marked stimulation of vascular cambial divisions with the formation of
considerable, but somewhat abnormal, secondary xylem. Kinetin treatment, in the presence or absence of added auxin, resulted in even more
marked cambial proliferation, with almost completely normal secondary
xylem development.
Initiation of secondary vascular tissue in roots appears also to be
under hormonal control, especially hormones moving from the aboveground portions of the plant into the root. The subject has been reviewed by Torrey (1963), and experimental evidence concerning the
essential role of auxin in cambium formation in isolated pea roots grown
in culture was given. Since isolated roots in culture do not usually form
any secondary tissues, the demonstration that excised roots can be induced routinely to form vascular cambium and extensive secondary
vascular tissues by providing them sugar and hormones via the cut
root base opens up the study of this aspect of hormonal control of
organization in roots. In roots of pea Pisum sativum, IAA at 10~
5 M
provided together with 8% sucrose via the root base led to cambium
initiation which progressed with time toward the root tip.
Loomis and Torrey (1964) applied the same technique to excised roots