Anatomy of Flowering Plants: questions with answers

A is a one-celled root hair, an extension of a root epidermal cell, that absorbs water and minerals; roots have no cuticle. B is a shoot trichome, usually many-celled, that helps reduce water loss.

Bean-shaped guard cells are common but not universal. The pore, paired guard cells and subsidiary cells together form the stomatal apparatus.

The stomatal apparatus is the pore together with its two guard cells and the subsidiary cells around them. Guard cells are generally bean-shaped, but in grasses they are dumb-bell-shaped.

Xylem and phloem share a radius, which defines a conjoint arrangement; in the usual collateral form, phloem is external to xylem. This arrangement is common in stems and leaves.

Open or closed status is decided by cambium, not by empty space. Without cambium the bundle is closed and lacks that cambial capacity.

A bundle is open when cambium lies between its xylem and phloem, and closed when there is none. Phloem outside xylem is true of both kinds, and no gap is involved.

The section shows a polyarch root with a large pith, identifying a monocot root. Monocot roots do not undergo secondary growth.

The epiblema is the outermost layer and may bear unicellular root hairs. The endodermis is the innermost layer of the cortex, not the surface layer.

Dicot roots usually have two to four xylem patches, a small pith and later cambial development that enables secondary growth. Monocot roots are polyarch with a large pith and do not undergo secondary growth.

The section shows the monocot pattern: numerous scattered bundles, smaller peripheral bundles and no cambium, so the bundles are closed. A dicot stem instead has open bundles in a ring.

In a typical dicot stem, vascular bundles form a ring and each bundle is open because cambium lies between xylem and phloem. In a typical monocot stem, the bundles are scattered and closed because this cambium is absent. “Open” describes the bundle’s cambium, not a gap in the ring.

A monocot stem has a sclerenchymatous hypodermis and a large, undifferentiated ground tissue with no separate cortex, medullary rays or pith. Its phloem has no phloem parenchyma, and its bundles often have water-containing cavities.

In a leaf vascular bundle, xylem is adaxial and phloem is abaxial. Ordinary bundles in a parallel-veined monocot leaf are generally similar in size, and turgid bulliform cells leave the section exposed.

The mesophyll is uniform rather than layered, and pores occur on both epidermides. The section therefore represents an isobilateral monocot leaf.

Dorsiventral palisade is adaxial, beneath the upper epidermis, with spongy tissue below. Isobilateral monocot mesophyll is undifferentiated and stomata occur on both surfaces.