Zea mays

3.10
3.12
A
B
3.10 Diagrams of fibrous sderenchymatous dements (with thick,
lignified seconduy walls) setn in (A) longitudinal and (B) transverse
views. These highly elongare cells have lapering (often branched) lips
and simple pirs are often frequem in tbeir walls. Fibres constitute a
major mechanical support syStem In the shoot.
3.12 Flowering specimens of the insectivorous dICOtyledon
Dros(!ra rotundifolitI (sundew). These were growing
on the pebble·strewn margin of a small lake in a very thin
soil which was deficient in minerals. panicularlr nitrogen
and phosphorus. Small insecl5 become trapped in the
mucilage secreted by numerous glands on rhe leaf surface
jci., 3. t t). The digestive enzymes in the secretion
breakdown the proteins in rhe insect and provide the plant
with an important sources of nitrogen and other minerals.
3.11 Leaf of the insec£ivorous dicotyledon
Droura rotundifolia (sundew d., 3.12). The
crowd«i long hairs, with glandular heads stick}'
....ith secretions, are especially prominent on the
adaxiallaminal surface. These epidermal glands
are complex multicellular Structures with the
qlindric.al stalk containing a cenrral rracheary
strand.
The epidermal cells of the glandular head
secrete a viscous fluid in which small insects
!xc::ome srock and the adjacent hairs then bend
towards the victim. Enzymes within the
secretion digest the insect's tissues and the
soluble products are absorbed by the gland and
tunslocated co the leaf and elsewhere in the
plant. (Copyright ofT. Norman Tml.)
3.13 Stack of cork harvested from the dicotyledon Quercus
suber (cork oak). This cork replaces the epidermis of
the young sum and represents the dermal srstem of the
tn:e. At intervals of about 10 years a layer several centimetres
thick (consisting of cork formed br successive cork
cambia) is removed from the tree but a min layer of newly
produced cork is left on the trunk to protect the phloem
within. Commercial cork is highlr water-resistant and
provides excellent thermal insulation.
65
3.11
3.13