1. Angiosperms IV Primary Growth: Roots and Stems

2. Roots and Root Systems Root Systems are often classified as either: –TAP ROOT SYSTEMS (found most commonly in eudicots) have prominent tap root and smaller branch roots

3. Root Systems –FIBROUS ROOT SYSTEMS (common in monocots) many similar sized roots in an extensive network

4. Functions of Root Systems Anchorage Storage Absorption Conduction Reproduction (occasionally)

5. Typical Eudicot Root

6. Young Root (cont.) Above the region of the meristem are the regions of elongation and region of maturation Meristem

7. Root Hairs Single epidermal cells with a long extension

8. Structure of an Older Dicot Root (cont.)

9. Functions of Root Structures ENDODERMIS –innermost layer of the cortex –functions in water regulation –cells are “belted” with a suberized layer called the Casparian strip –waterproofs the layer so water must move through the cells (not the walls) into the stele

10. Endodermis

11. Functions of Root Structures (cont.) PERICYCLE –source of cells for formation of branch (lateral) roots –involved in formation of cambial layers in woody roots –endogenous growth of branches

12. Functions of Root Structures (Cont.) PHLOEM –transport of nutrients XYLEM –protoxylem (first to mature in the root) –metaxylem (last to mature) –water and mineral conduction CAMBIUM (with pericycle cells will form vascular cambium in woody root)

13. Root Modifications Storage tap roots (radish, jicama, carrots)

14. Root Modifications (cont.) Fascicled storage roots (yams, sweet potatoes, cassava) Casava for sale Sweet Potatoes

15. Sweet Potato vs.Yam Impomea batatas (sweet potato) Diascorea batata (yams)

16. Root Modifications (cont.) Prop roots (corn)

17. Root Modifications (cont.) Aerial roots (Spanish moss, orchids) Aerial roots on an orchid

18. Root Modifications (cont.) Pneumatophores for gas exchange on white mangrove plants

19. Eudicot Stem Structure (cont.) Leaf primordia with trichomes Axillary (lateral) buds –give rise to branches –exogenous development

20. Structure of a Eudicot Stem Apical Meristem (shoot apex, shoot tip) –composed of tunica and corpus layers –tunica gives rise to protoderm –corpus gives rise to procambium and ground meristem

21. Older Eudicot Stem (xs) Epidermis Collenchyma or fibers Cortex Vascular bundles Pith

22. Eudicot Stem Vascular Bundle Bundle cap (composed of fibers) Phloem Fascicular cambium Xylem

23. Monocot Stem Scattered vascular bundles (atactostele) Surrounded by parenchyma cells (ground tissue)

24. Monocot Vascular Bundle Sheath of fiber cells Phloem with obvious companion cells Large metaxylem vessels Air space

25. Stem Modifications T endril (may also be a leaf modification) Rhizome Stolon or runner Cladophyll Thorn Prickle Spine (leaf modification) Tuber Corm vs. bulb (leaf modification)

26. Tendrils Leaf or stem modifications for attachment

27. Rhizomes Underground, horizontal stems

28. Stolon or Runner Above ground horizontal stems –Seen in strawberry plants

29. Thorns Thorns are modified branch systems Crategus Locust tree

30. Spines Spines are modified leaves

31. Prickles Epidermal structures found in roses and other plants

32. Tuber Underground, storage stem (a white potato)