1. Lecture 3 Roots and Stems
Zivuku. M, 2015
Lecture 3 Roots, Stems, Leaves

2. STRUCTURE OF MODIFIED ROOTS AND STEMS
AIM – be able to:
Differentiate between monocots and dicots roots
Discuss and sketch the external and internal structure of roots and stems , Longitudinal and cross sections through both monocotyledonous and dicotyledonous roots
Describe the function and give examples of different kinds of modified roots and modified stems.

3. Dicotyledonous roots
Xylem “arms” X to conduct water and dissolved nutrient minerals
Phloem between “arms” to transport dissolved sugar (sucrose)
Vascular cambium between xylem + phloem

4. How do Monocotyledonous roots differ ?
Monocotyledonous roots have a central pith
Different arrangement of vascular tissue –Xylem in a ring
No vascular cambium

5. Dicotyledonous vs Monocotyledonous

6. Modified roots – Food storage
Tap roots – Carrots, beetroot
Lateral roots - Tubers
Sweet potatoes

7. Modified roots – Aerial Prop roots
Prop roots – Adventitious roots from base of stem to give extra support e.g. Mielies, Zea mays

8. Modified roots – Aerial Buttress roots
Shallow roots in moist forests to absorb dissolved nutrient minerals from decomposing leaves
Buttress roots support shallowly rooted trees in damp soil and can cover large areas
e.g. Ficus sycomorus
+ Ficus burkei

9. Modified roots – Aerial Clinging roots
Aerial roots to anchor plant to bark or branch of another plant
e.g. Climbing plants and some
epiphytes
e.g. Philodendron monstera

10. Modified roots – Aerial Crampons
Short adventitious roots for climbing = Crampons
e.g. Hedera helix - Ivy

11. Modified roots–Aerial Pneumatophores
In intertidal mangroves, roots above the tide – pneumatophores can “breathe” to allow oxygen to reach submerged roots in anaerobic soil

12. Modified roots – Strangler roots
Strangler figs start as epiphytes, long aerial roots grow down to the ground to anchor the tree.
As a tree it competes with its host for light + nutrients
Eventually the mesh of roots strangle/smother + kill the host by crushing the secondary phloem

13. Modified roots – Photosynthetic roots
some epiphytes
e.g. Phalaenopsis
Moth orchid

14. Modified roots –Contractile roots
Plants with corms or bulbs (underground stems) have wiry roots that pull them deeper into the soil each season to keep them firmly underground. e.g. Gladiolus

15. Modified roots- Parasitic roots
Stem parasites - epiphytes e.g. Tapinanthus oleifolius, mistletoe and Dodder, have special “roots” to penetrate the host plant to absorb water – Houstorium Root parasites – e.g. Striga, Dodder, Rafflesia

16. Stem structure – Dicotyledonous vs Monocotyledonous stem

17. Terminology

18. Modified stems – Stolons + Tendrils
Stolons - Horizontal stem /runner e.g. Fragaria
Roots + new shoot at each node
Tendrils e.g. Vitis

19. Modified stems – Underground stems Rhizomes and Corms
Rhizomes e.g. Iris, Phragmites
Adventitious pull roots
Survive unfavourable season Corms e.g. Gladiolus

20. Modified stems – Underground Tubers + Bulbs
Tubers e.g. Solanum Potatoes
Bulbs e.g. Allium, Onions, Crinum paludosum

21. Modified stems- Cladodes
Fleshy stems that photosynthesize and store water New plant can grow vegetatively from cladode e.g. Euphorbia virosa, Opuntia spp. Spines are modified leaves, stiff, slender, sharp stuctures that develops from below the epidermis

22. Modified stems – Thorns
Gymnosporia buxifolia Carissa bispinosa
Thorns are modified stems that can have leaves + flowers on them – stiff, woody, sharp modified stems

23. THANK YOU
FOR YOUR ATTENTION