SECONDARY GROWTH IN ROOTS-5

Fleshy Roots with Secondary Growth

Center of an Lupine Root with Secondary Growth.

Secondary Xylem & Phloem may contain large amounts of storage Parenchyma. Roots like carrot & radish contain nutrient rich secondary Parenchyma. During secondary growth, cell divisions can occur in parenchyma cells of the secondary vascular tissues to such an extent that the primary xylem becomes disorganized, and its original position is hard to determine. Fibers may be present in both xylem and phloem. However, they may be sparse and their cell walls may be unlignified.

Medicago (alfalfa) Root

Low magnification view of Secondary Growth in the Root Center	Cross-sections through roots of Alfalfa (Medicago sp.)
Low magnification view of Secondary Tissues: The Xylem is obvious and has thick Rays. The Phloem is located just outside the Xylem but is hard to see.	Magnified area of Secondary Xylem: Note the large Vessel Members, smaller Tracheary Elements, Parenchyma and unlignified Fibers.

Secondary Phloem in fleshy roots usually has lots of Parenchyma
but it may closely resemble the Phloem in Stems.

Papaya Root


Secondary Phloem of Papaya Root stained with Toluidine Blue: Note the Lignified Fibers	Outer Part of a Papaya Root: Note the abundance of Parenchyma!
*Locate the Periderm!!!*

Transect of a Carrot Root!

There is an Epidermis. This is followed by a large Parenchymatous Cortex. Secondary Phloem Vascular Cambium Secondary Xylem Primary Xylem at the Center All of these internal tissues contain lots of soft Parenchyma cells.
Autofluorescent Image from the center of a Carrot Root with a small amount of secondary growth.

Radish (Raphanus) Roots

Young Radish (Raphanus) Root with Secondary Growth: Note the preponderence of Parenchyma.	Older Radish Roots: The Primary Xylem can be found at the center of the axis.

Older Radish Root: Note the extremely wide Rays and the abundance of Parenchyma.

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