Page 155 - Biology_F5

Biology for Advanced Level Secondary Schools

microspores (pollen grains) and annual rings of the xylem. The constituent
megaspores (ovules) are produced. tissues of these species have resin canals
(b) The pollen grains are winged to provide which run vertically and laterally along
buoyance, hence they are wind pollinated. the stem. The bark, has secondary phloem,
(c) They have seeds that are not enclosed which is relatively thick and does not have
within the ovary; thus, they have no companion cells, but albuminous cells that
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ovaries, and no formation of fruits. perform the same function as the companion
cells.
(d) Their xylem lacks vessel elements but
has only tracheids as the conducting The trunk has a tap root system with
elements. lateral roots in different directions. Roots
(e) Their phloem tissues are associated with of some Pinus form symbiotic association
albuminous cells instead of companion (mycorrhizae) with fungi. Young shoots
cells. have two types of leaves; small scaly
(f) The majority of members of leaves on the main stem and leaves on the
Coniferophyta produce resin in special dwarf shoots. In addition, the plant has
ducts called resin canals. Such resin is foliar spars, which develop into normal
useful in wound healing and deterring branches. The fertile plant bears female
browsers. and male reproductive cones, which are
(g) Most members of Coniferophyta are distinct when mature. The male cones
evergreen plants with needle-like shaped are relatively soft or herbaceous and
leaves. small, while female cones are woody and
relatively larger. Usually, male cones are
Structure of Pinus borne on the lower branches, while female
The sporophyte consists of roots, stem and cones are borne on the upper branches
branches, bearing needle-shaped leaves, (Figure 3.27(b)). The leaves enclosing the
which appear in clusters of two to five. cones are called sporophylls. For instance,
These clusters are called fascicle. Their microsporophylls are associated with
leaves are dark green with cuticle, sunken male cones, whereas megasporophylls are
stomata, and resin canals in the mesophyll. associated with female cones.
Their stems develop relatively wider

Female cone

Female cone Seed

Male cone

(a) (b)

Figure 3.27: General structure of (a) female cone and seeds and (b) Pinus plant

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