1. Secondary Growth

2. Tree Rings
Rings visible in heartwood and sapwood are regions of early and late wood
Early wood forms during wet springs
Late wood indicates a dry summer or drought when no large-diameter xylem cells were made for water uptake
In most temperate zone trees, one ring forms each year

3. Early Wood and Late Wood
vessel in xylem
direction of growth
early
late
early
late
early
late
early
late
early
B Early and late wood in an ash tree. Early wood forms during wet springs. Late wood indicates that a tree did not waste energy making large-diameter xylem cells for water uptake during a dry summer or drought.
Fig b, p. 409

4. Secondary Growth
In many plants, secondary growth thickens branches and roots during successive growing seasons
Extensive secondary growth of eudicots and conifers produces wood
Tree rings can be used to study past environmental conditions

5. Variations on a Stem
Specialized stems allow some plants to store nutrients, to reproduce sexually or asexually
Specializations include stolons, rhizomes, bulbs, corms, tubers, and cladodes

6. Stolons
Stolons (runners) are stems that branch from the main plant stem
Adventitious roots and leafy shoots sprout from nodes and develop into new plants
Example: strawberry

7. Rhizomes
Rhizomes are fleshy, primary stems that grow under the soil, parallel to its surface
They are the plant’s primary storage tissue
Example: turmeric

8. Bulbs
A bulb is a short underground stem with overlapping layers of thick, modified leaves (scales)
Contains starch and other stored products
Example: onion

9. Corms A corm is a thickened underground stem that stores nutrients
Unlike a bulb, a corm is solid rather than layered
Example: taro

10. Tubers Tubers are thickened portions of underground stolons
They are the plant’s primary storage tissue
Example: potato

11. Cladodes
Cladodes are flattened, fleshy, photosynthetic stems that store water
Example: cactuses

12. Key Concepts Modified Stems
Certain types of stem specializations are adaptations for storing water or nutrients, and for reproduction

13. Tree Rings and Old Secrets
Many trees form one ring each year
Tree rings hold information about environmental conditions that prevailed while the rings were forming
Example: Relative thicknesses of rings reflect the availability of water – rings show that settlers who arrived at Roanoke Island in 1587 suffered a major drought

14. A Record of Rainfall
A section of a bald cypress tree that was living near English colonists when they first settled in North America – narrower annual rings mark years of severe drought

15. Tree Rings and Old Secrets
Tree rings are used to date archaeological ruins; gather evidence of wildfires, floods, landslides, and glacier movements; and study the ecology and effects of parasitic insect populations

16. Tree Rings and Old Secrets
year: 1 2 3
p. 411

17. Some Tree Rings