Instant Notes: Plant Biology

surrounding tissue. Metaxylem cells form after elongation has ceased and have

more complex secondary thickening. Ray cells radiate from the vascular

cambium of roots or stems of woody plants and permit lateral movement of

water.

Phloem tissue has two cell types. Sieve tubemembers form an elongated

pipe, the sieve tube. The cells are living and are linked through perforations in

adjoining end cell walls (the sieve plate). The cytoplasm of these adjoining cells

also connects, and transport of solutes takes place through it (Topic H4). Sieve

tube members have no nuclei, but retain other functional organelles. The other

cell type is the companion cell, which have many mitochondria and provide

energy required for phloem transport (Topic J4).

26 Section C – Vegetative anatomy

Sieve plate

Sieve tube member

Companion cell

Phloem

parenchyma

(a) (b) (c)

Fig. 2. Structure of phloem and xylem.