Lesson 4 of 10 · 9 min
Vascular bundles
NCERT §6.1.3, Figure 6.2
Meera now has three sections on her slide: a sunflower root, a sunflower stem and a maize stem. In all three she can find xylem and phloem, but they sit together in completely different ways.
The lesson in notes
In short
Xylem and phloem are complex tissues; together they make up a vascular bundle.
Open bundle: cambium lies between phloem and xylem, so the bundle can later add secondary xylem and phloem. Found in dicot stems.
Closed bundle: no cambium, so no secondary tissues form. Found in monocots.
Radial arrangement: xylem and phloem lie in separate patches on different radii, alternating round the centre. This is the root pattern.
Conjoint arrangement: xylem and phloem lie together on the same radius. This is common in stems and leaves.
In a conjoint bundle the phloem is usually only on the outer side of the xylem.
Combine the two words for a full description: dicot stem bundles are conjoint and open; monocot stem bundles are conjoint and closed; root bundles are radial.