Wednesday, February 23, 2011

Lab 5 - Leaves and Modifications

B. Leaf Blades

Syringa (lilac) prepared slides are examine.

x10. Leaf of a lilac.

Mid-vein in a lilac leaf. 
Note mid-vein is supported by cells with thickened walls above and below.

Variation in leaf blades: 
1) Sun versus Shade Leaves
Prepared slides of leaves.

'Sun leaf'.

'Shade leaf'.

Compare to 'shade leaf', 'sun leaf' is thicker, with a smaller blade area and has more layer of palisade mesophyll, and more xeromorphic (maybe be affected by water relations) .

2) Maturity of plant
Plants like Hedera (English Ivy) have different leaf shapes in juvenile and mature stage.

Juvenile English Ivy has five-lobed leaves on the climbing vine.

Mature English Ivy has thicker leaves without lobes.

3) Habitat
a) Mesophytic leaf  - moderate habitats
- cuticle over epidermis
- more stomates on the lower leaf surface
- has adaxial palisade and abaxial spongy layers

Lonicera (honeysuckle) is one of the examples of plants that have mesophytic leaf.

Adaxial side of the lead.

Abaxial side of the leaf. 

Note that there are both xylem and fibre. 
Xylem has thinner cell wall compare to fibre.
Xylem is on the adaxial side of the leaf (below palisade mesophyll).

Corn also has mesophytic leaf. 
Corn, like other grasses, the mesophyll does not differentiate into spongy and palisade layers.

Kranz anatomy: 
The arrangement where there is a ring of 
large, chloroplast-containing bundle-sheath cells 
surrounding the vascular bundle. 
(Not clear in this picture.)

b) Xerophytic leaf - Dry habitats
- thick cuticle
- sunken stomates
- more palisade layer
- less spongy layer

Cycad has compound leaves. So a cross-section of the leaflets does not have mid-rib, but mid vein.

Cycad leaf cross-section.

Adaxial side of the leaflet. x40.

Subsidiary cells overarch the stomata. x40.

3) Hydrophytic leaf - wet or submerged habitats
- submerged leaves lack stomates
- air cavities

Water lily leaf cross sections are examined.

The chloroplasts are red in colour.

Stoma only found in the adaxial surface of the lily leaf.

C. Trichomes
Adaxial side of the leaf of Viburnum rhytidophyllum.

The trichomes are found in the abaxial side of the leaf.

The trichomes are branching. What is the function? Protection and water regulation.

Larger magnification of the trichomes.

D. Leaf Appendagges
Stipules of the Begonia.

E. Shoot Modifications

1. Storage (water)
- parenchyma that has no chloroplasts; large, living, thin-walled, large vacuoles with watery or mucilaginous contents.

Peperomia glabella (wax privet peperomia) has multiple epidermis.

Multiple epidermis of large, thin-walled parenchyma cells that lack chloroplasts. 
The oil sac are yellow in colour.

Aloe is a desert plant has water storage tissue within the photosynthetic tissues.

The colourless water storage tissue is slimy due to mucilage.

2. Protection
Thorn - stem
Spine - leaf
Prickle - epidermis

Citrus medicata (citron) has thorns.

Older citron tree.

The cross section of a thorn resemble that of the stem.

Euphorbia has spines (modified leaf).

Rubus (blackberry) has prickles.

No vascular bundle is observed in prickles.

3. Support
Peas' tendrils are modified leaf as they replace the terminal leaflets.

Passiflora (Passion flower) has modified branch as tendril. Its tendrils grow from the leaf base (axillary bud).

4. Vegetative reproduction
Kalanchoe form plantlets as a mean of vegetative reproduction.

5. Overcoming Nitrogen Deficiency: insectivourous plants

Sarracenia (Pitcher plant):
- nectar-secreting glands
-downward-pointing hairs and waxy inner surface
-enzymatic fluid

Dionaea (Venus Flytrap): trigger hair.

Pink secretory cells that secrete digestive enzyme in Dionaea.

Drosera (sundew) has sticky mucilage and red-coloured to attract insects and the tentacles traps the insects when the insects touch the tentacles.

Utricularia vulgaris (Bladderwort)
I don't have a picture.
- Yee Sing

Tuesday, February 22, 2011

Lab 4 - Stems: Structure and Function


A square stem of a Coleus plant. The aerial part of the plant is the shoot which includes the stems as well as the leaves. *look into lab 5 blog posting for information on leaves. 

The specific regions where leaves, buds and breaches arise are called nodes. The stem connecting two nodes is the internode.

Two halves of a bean seed minus its seed coat. When the seed germinates the cotyledons become two embryonic leaves, the radicle grows into the embryonic root and the plumule develops into the shoot.

A longitudinal section through the shoot tip of Coleus prepared slide. A magnified version of the red box is in the next picture. Can you name the following terms without looking into your notebooks? Protoderm, ground meristem, procambium, Leaf primordium, apical meristem, trichome and bud primordium. Scroll to the middle of this page to find the answer.

The photo from the red box above. These are scalariform vessels and tracheids of the xylem. However, they look more helical/spiral than sclariform.

Prepared slide stem cross section of Ranunculus (buttercup). Buttercups have closed vascular bundles meaning all of the procambial cells have differentiated (ie. are all used up). They do not exhibit secondary growth because no further differentiation is possible. Note the parenchymatous cortex and pith. The vascular bundles are located in a circle in the stem. The primary phloem is to the outside and the primary xylem is to the inside. The division of the xylem is from the inside out and thus the the development is endarch

The above a stem cross section of Riciinus (castorbean) that is starting secondary growth. The layer of cells outlined in red is the interfasicular cambium. Above this layer are clusters of phloem tissue and the large cells below are xylem vessels. 

Here is zoomed out view of the interfasicular cambium.

Labeled longitudinal section of Coleus. The location of the bud primordia is also known as the axil. The outer several layers of the apical meristem is the tunica layer and underneath this layer is the corpus layer.

Stem cross section of Sambucus. If this picture were to continue inward, it would show the primary xylem at the end of the secondary xylem. And further inward would be the pith.

Didn't get a good section of Pelargonium.  : (

Prepared slide of Tilia (basswood) stem cross section.

Prepared slide of Zea mays (corn). Corn is a monocot and do not engage in secondary growth (characteristic of monocots). It has its vascular bundles scattered throughout its stem.