The document discusses the root-stem transition zone in plants. It begins by explaining that the root has a radial vascular structure while the stem has a conjoint structure, so there must be a region where these structures merge. This region is called the root-stem transition zone. The document then describes four types of root-stem transitions (Fumaria, Cucurbita, Lathyrus, and Anemarrhena) which differ in how the xylem and phloem structures divide and rearrange as they transition from root to stem. Finally, it notes that the transition zone represents a different internal arrangement than the root or stem and reflects different evolutionary stages in the development of the vascular system.

1. ROOT STEM TRANSITION
BY
HETAKUMARI PILUDARIA
BSc (HONS) BIOTECHNOLOGY
SEM II

2. INTRODUCTION
 Root and stem form a continuous structure in plants called the axis.
 The vascular tissue in root is radial (xylem and phloem arranged
separately in different radii) whereas in the stem is conjoint (xylem
and phloem are arranged together in same radii as vascular bundles).
 Thus, there should be a region in the axis where the vascular
structures of the root and the stem meet and merge together.
 This peculiar region is called the Root-Stem Transition Zone.
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3.  The epidermis, cortex, endodermis, pericycle and the secondary
vascular tissue are continuous from root to stem.
 Only the primary vascular tissue in the axis undergoes a change in
their position and orientation.
 The exarch arrangement of xylem in root changes to endarch position
in the stem.
 In the transition zone, the vascular tissue undergoes many changes
such as Forking, Rotation and Fusion.
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4.  The vascular tissue also increases their diameter.
 The exact position of the transition zone is different in different plants.
 Usually, the transition zone occurs at the tip of the radicle or at the
basal or middle or at the top portion of hypocotyl.
 The length of transition zone also varies from few millimeters to
several centimeters.
 The transition of vascular tissue may be gradual or abrupt in different
plants.
 The phloem tissue, in most of the cases, remains more or less same
position.
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5.  Different types of Root Stem Transitions are observed in plants
 Eames and MacDaneal (1947) described FOUR types of root stem
transition in plants.
 They are:
(1). Fumaria Type (A – Type)
(2). Cucurbita Type (B – Type)
(3). Lathyrus Type (C – Type)
(4). Anemarrhena Type (D -Type)
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6. FUMARIA TYPE ROOT-STEM TRANSITION (TYPE A)
 Occurs in Fumaria, Mirabilis and Dipsacus.
 Each xylem strands in the root divides radially into two branches.
 As the branches go upward they swing laterally.
 Among these two branches, one swing to the right and one swing to
left and join to the phloem strand inside.
 Phloem strand do not change its position or orientation and they pass
directly from the root to the stem.
 The number of vascular bundles formed in the stem will be equal to
the number of phloem strands occurs in the root.
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7. HPILUDARIA
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8. CUCURBITA TYPE ROOT-STEM TRANSITION (TYPE B)
 Found in Cucurbita, Acer, Phaseolus and Tropaeolum.
 In Cucurbita type both the xylem and phloem strand divide into two
strands.
 Each xylem swing as in Fumaria type, and join with a strand of
phloem.
 Phloem does not change its orientation, but the xylem becomes
inverted.
 Number of vascular bundles formed in the stem will be twice the
number of phloem strands in the root.
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9. HPILUDARIA
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10. LATHYRUS TYPE ROOT-STEM TRANSITION (TYPE C)
 Found in Lathyrus and Medicago.
 Here the xylem strand does not divide but pass continuously into the
stem.
 However the xylem strands twist 180 degrees.
 Meantime the phloem strands divide.
 The phloem strands then move laterally to the position of the xylem
strand and then they fuse together and join the xylem strand on the
outside
 In this type the number of vascular bundle formed in the stem will be
equal to the number of phloem strands found in the roots.
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11. HPILUDARIA
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12. ANEMARRHENA TYPE ROOT STEM TRANSITION (TYPE D)
 It is a very rare type of root-stem transition.
 Found in some monocot plants such as Anemarrhena.
 Here half of the xylem strand divide radially, the rest remain undivided.
 The branches of the divided xylem swing laterally and join with the
undivided xylem strand which has now inverted its position.
 The phloem strands do not divide but fuse in pair with the xylem
strand.
 Thus a single vascular bundle in this type of stem composed of two
phloem strands and three xylem strands.
 The number of vascular bundles formed in the stem will be half the
number of vascular strands in the root.
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13. HPILUDARIA
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14. S
U
M
M
A
R
Y
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15. SIGNIFICANCE OF ROOT-STEM TRANSITION
 In the transition zone the internal tissue arrangement is completely
different from that of root and stem.
 Thus, this region does not belong to any of those categories.
 Several interpretations are available to describe the structure and evo-
lutionary significance of the transition zone.
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16.  The root and shoot tips of the seedling have their own meristem which
forms the root and stem, respectively.
 During development, vascular connections are established between
radicle and cotyledon via hyopocotyl.
 The epicotyl traces are joined with the radicle-hypocotyl-cotyledon
unit and tissues between the traces are mutually accommodated
(Esau, 1965).
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17.  The radial arrangement of xylem and phloem is usually considered as
primitive whereas the collateral arrangement of them is regarded as
advanced.
 Therefore, the xylem and phloem arrangements at the upstream
transition zone represent the different evolutionary stages which
culminate into collateral arrangements in the stem.
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18. THANK YOU
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