Budburst Lab: Characteristics of leaves, buds, and twigs

Objectives for this lab: learn to recognize and name stem anatomy learn the parts of a leaf learn to recognize and interpret leaf arrangement, and simple and compound leaves become familiar with leaf shapes, margins, arrangements,  and the terms that describe these features examine and learn to recognize different types of trichomes (plant hairs) learn to recognize and name plant growth patterns

This lab deals with characteristics of the vegetative parts of a plant (buds, twigs, and leaves). Study your tree branch sample with a partner.  Complete the lab sheet.

1.  STEM ANATOMY

Bud--A compressed, undeveloped shoot.  Buds may be lateral or terminal.
Node-- the point on the stem where leaf or bud is. The space between two nodes is an internode
Leaf scar--a mark remaining on the stem where a leaf was attached
Bud scale -small structures that cover the bud.  Bud scales are actually modified leaves.
Bud scale scar--a mark on the stem where a bud scale was attached. When the terminal bud sprouts and its scales fall off, growth rings are formed. The portion of a stem between two sets of growth rings indicates one season's growth.
Pith--the spongey tissue in the center of a stem or twig. Pith can be solid, chambered, or diaphragmmed.
Lenticel--a "breathing pore" in the skin or bark of a stem.

2.  PARTS OF A LEAF

Petiole--the stalk of a leaf; a leaf without a petiole is called sessile
Blade--the flat, expanded portion of the leaf
Vein -  a rib or ridge in the middle of a leaf.  Veins are tissues that carry water and food in the plant.
Stipule-- a flat, often leaf-like flap below a leaf. Not all leaves have stipules. Stipules can be highly modified into spines, scales, etc.
Axillary bud--the bud in the angle between the leaf and the stem.
Helpful Hint: Remember to look for stipules below the petiole and an axillary bud above the petiole.

3.  LEAF ARRANGEMENT

Alternate--leaves arranged one per node
Opposite--leaves arranged two per node
Whorled--arranged two or more per node
Fascicled--leaves grouped in small, tight bundles, eg., pine needles bundled into clusters of 2 or 3

4.  SIMPLE AND COMPOUND LEAVES

Simple--the blade is all in one piece, though it may be lobed, toothed, etc.

Compound--the blade is divided all the way to the midrib (rachis) into two or more pieces.
Once pinnately compound--leaflets arranged along one undivided main axis.  A leaf is even pinnately compound (paripinnate) if the leaflets are in pairs with none left over (as in the linked image.)  A leaf is odd pinnately compound (imparipinnate) if the leaflets are in all in pairs except one left over at the tip.
Twice pinnately compound--main axis (rachis) with two or more branches and the leaflets arranged along the branches. The branch divisions are primary leaflets and the ultimate divisions are secondary leaflets. There can also be thrice-pinnately compound leaves,etc.
Palmately compound--leaflets all arising from one point at the base of the leaf.

5.  VENATION - how the veins are arranged

Pinnate--with a main midvein and secondary veins arising from it at intervals
Palmate--with the main veins all arising from one point at the base of the leaf.
Parallel--with all the main veins parallel (usually also parallel to the sides of the leaf.)
Dichotomous--with each vein branching in two again and again (e.g. Ginkgo)

6.  MARGINS

Entire--smooth, with no teeth or lobes 
Serrate--with sharp, forward-pointing teeth
Doubly serrate--with teeth which have smaller teeth on them
Serrulate--with very tiny sharp teeth
Dentate--with teeth which point outwards
Crenate--with low, rounded scallop-like teeth
Undulate--waving up and down
Revolute--turned under
Crisped--curled tightly (e.g. parsley)
Spinose--with stiff points
Lobed, parted, divided, cut, etc.--A number of terms describe the various degrees of lobing. Different sources use the terms in different ways. Lobed is usually the least divided and pinnatifid or palmatifid usually the most--cut almost all the way to the midrib.

7.  PLANT SURFACES and TYPES of HAIRS

glabrous surface - without hairs
Glaucous surface -glabrous and with a coating of wax
Surface has trichomes -  hairs on the surface of the plant.


TYPES of HAIRS (trichomes)


Simple hairs-- straight and unbranched
Stellate hairs--shaped like stars.  The rays may be free or fused
Glandular hairs--topped with a gland or swollen and gland-like.  You may also see stalked glands--glands with stalks stiffer than hairs
Branched hairs--the main hair has side branches (look at the hairs on the midrib of the leaf)
Plumose hair or bristle--the main hair has side hairs (the smaller side hairs are just visible on each big hair)
Scale--a thin, flat structure (like a fish scale), often attached in the center
Ciliate--with short hairs around the margin
Pilose--with long, soft, spreading hairs.  Here is another example.
Pubescent--with short, soft hairs  (This term is sometimes incorrectly used to refer to having hairs of any sort)
Scabrous--rough or sandpapery, with very short, stiff hairs or projections (Examine the close up shots of the leaves and stem)
Tomentose--with a dense, soft coat of hairs that is hard to see through, e.g., underside of mustang grape leaves

Annual--plant which lives for one year or season, reproduces, and then dies
Biennial--plant which lives for two years or seasons, reproduces, and then dies
Perennial--plant which lives for several to many years or seasons. Perennials may be woody, with stems that persist aboveground over the winter, or they may be herbaceous, with stems that die back to the ground each year.
Evergreen-having leaves which persist for two or more seasons. Broadleaf evergreens usually have thick, leathery leaves.
Deciduous--having leaves which die and fall in the cold or the dry season


Adapted from VEGCHAR at http://www.csdl.tamu.edu/FLORA/tfplab/vegchar.htm   April 19, 2007