BI 266 Plants Notes Fall Term 2013
1) The “plant blindness” syndrome
"the inability to notice plants in one's own environment, leading
to the inability to recognize the importance of plants in the
biosphere and in human affairs." [Wandersee and Schussler 1999,
“The lovable mammals and lifeless plants” (Lindemann Matthies 2005
Plants can communicate by: Mycorrhizal connection
Plants can recognize one another
Plants can “see” other plants; Plants can make “intelligent” decisions
Plants can defend them selves physically and chemically
Plants can speak foreign chemical languages
Plant Duration (The life span of an individual plant)
1) Herbaceous plants
E.g. Arabidopsis thaliana
Annual plants live for a single growing season during which they germinate, grow
vegetatively, form flowers, and produce fruits and seeds. Biennial
E.g. Verbascum thapsus: mullein st
Biennial live for two years; plants are vegetative in the 1 year and produce
flowers/fruit/seeds in the 2 year.
E.g. Trilium grandiflorum
Perennial live for three or more years and usually flower and fruit yearly once plants
get to maturity. 2) Woody plants: are always perennial
Trees have mainly Lianas are woody but
Shrubshave multiple stems
one single stem they cannot sustain
“the trunk” themselves, therefore,
they need a physical
1. An annual plant... support (e.g. other plants,
a. is a plant with annual growth rings. rocks, etc.)
b. lives for several years; it flowers and produces
c. lives for two years; it flowers and produces fruits/seeds only once in
the 2nd year.
d. lives for several years; it flowers and produces fruits/seeds only
once in life, after which it dies.
e. lives for one growing season; if flowers and produces seeds in the
same year, after which it dies.
f. is a plant that has a stomatal annus, equivalent to the anus of
Ephemeral pl.: live
for 23 weeks; E.g.
Extremely longevive pl.: can live thousands
e.g. Giant sequoia Special case: monocarpy; e.g. Agave spp.
Monocarpic plants are perennial but produce flowers and fruits only once after which
they die; for example, Agave spp.
“Simple” [consist from one type of
cells]-produced by meristems
Tissues Classification 2. Parenchyma
1. Meristems Tissues produced by
Group of cells that
Group of cells
are completely that develop
unspecialized. “Complex” [formed from several types of
undergoing mitosis with certain cells]
creating other cells characteristics in 5. Xylem
that will become order to be 6. Phloem
specialized. specialized for a 7. Epidermis
specific role 8. Periderm
Are small and very 9. Secretory cells & tissues
Cancer in plants is rare due to the fact that mitosis is done in a very controlled and precise
From this to...
To this... Meristems are responsible for plant growth and development, which are the result of
mitotic cell divisions. Meristematic cells are the least differentiated cells; they are small
and densely packed together, with no intercellular spaces. Their cell wall is thin. They
have a dense protoplasm; their vacuoles are very small; they lack differentiated plastids
(e.g., chloroplasts, chromoplasts).
Meristems can be found at the embryo of a seed, for example, this oak tree. There are
many types of meristems that grow this tree.
classifications: Primordial: characterize the embryo; in a mature pl, they can be found in the apical
meristems(root and shoot tips) (Found in the embryo, all cells in the embryo are primordial,
so they can become any kind of cell.
Based on their oPrimary: are produced by the primordial meristems and they generate primary tissues (which in
their totality form the “primary structure” of a plant).
Secondary: develop from mature, primary tissues through cell dedifferentiation; produce
secondary tissues (“secondary structure”).
Based on their position
Apical: are primordial meristems
Lateral: they are secondary meristems:
Intercalary: found at the stem nodes
Cork Cambium Lateral Meristems
Secondary meristems generate growth in thickness
Vascular cambium produces secondary xylem toward the interior and secondary phloem
at the exterior
[“interior” = towards the center of the stem; “exterior” = towards the exterior of the
Cork cambium produces the periderm (bark). 2. Parenchyma
Where starch and
other sugars are Found in leaves Aerenchyma
stored Found in aquatic plants
chloroplast Something an aquatic plant
is responsible for uses to store air
top pic shows the spaces
between cells where the air
Parenchyma Tissue: Composed of parenchyma cells, which are the most abundant of the
cell types and are found in almost all major parts of higher plants.
Parenchyma cells assume various shapes and sizes, with the majority having 14 sides.
Tend to have large vacuoles and may contain starch gains, oils, tannins (tanning or dyeing
substances), Crystals, and various other secretions.
Parenchyma without Chloroplasts mainly function in food or water storage, For
example, the stoft edible parts of most fruits and vegetables consist largely of
Some parenchyma cells deveop irregular extensions of the inner wall that greatly
increase the surface area of the plasma membrane. Such cells, called TRANSFER 3. Collenchyma
“Supporting” function: living tissue that originates from parenchyma cells in which the
primary walls (most commonly) become thickened at the cell corners with cellulose.
Usually a primary tissue. Often found in the ribs of stems and petioles, immediately
under the epidermis – provides elasticity (e.g., in such a way herbaceous stems or leaf
petioles do not break when the wind blows).
usually derived from parenchyma
recognize it by its cell walls that are thickened with cellulose inside them
Hold their own weight.
have living cytoplasm and may remain alive a long time. Their walls are generally
thicker and more uneven in thickness than those of parenchyma cells. Uneveness is due to
extra primary wall in the corners.
Often occur just beneath the epidermis; typically are longer than they are wide, and their
walls are pliable as well as strong.
provide flexible support for both growing organs and mature organs, such as leaves and
floral parts. E.g) strings of celery are composed of collenchyma cells. 4. Sclerenchyma 4.1. Sclereids
Sclerenchyma has a “mechanical” function: dead tissue, much more specialized and
diverse than collenchyma. Primary walls of sclerenchyma cells become very thickened
with lignin, and as a result cells are dead at maturity. Can have primary or secondary
Sclereids: Length and width more or less equal.
Fibers: Length much, much longer than width (cells are very long).
Sclerenchyma Tissue: Consists of cells that have thick, tough, secondary walls, normally
impregnated with LIGNIN.
Most sclerenchyma cells are dead at maturity and function in support.
2 forms of Sclerenchyma occur:
1)Sclereids ; maybe randomly distributed in other tissues. E.x) the slightly gritty texture of
pears is due to the presence of groups of sclereids. Hardness of nuts shells and the pits of
peaches and other stone fruits is due to sclereids.
tend to be about as long as as they are wide and sometimes occur in specific zones, rather
than being scattered within other tissues.
2) FIBERS: May be found in association with a number of different tissues in roots, stems, Fibers
Sclerenchyma does not exist in:
a. The roots of some plants
b. The stems of some plants
c. The leaves of some plants
d. The meristems
e. The pear fruit
Some important tissues are always composed of two or more kinds of
cells and are referred to as COMPLEX TISSUES.
2 most important complex tissues in plants are XYLEM and
PHLOEM; function primarily in the transport, ions and soluble food
(sugars) through out the plant.
some complex tissues are produced by apical meristems
most complex tissues are produced by the vascular cambium and are
often referred to as VASCULAR TISSUES. Epidermis, which forms a protective layer covering all plant organs,
consists primarily of parenchyma or parenchymalike cells, also
OFTEN includes specialized cells involved in the movement of water
and gases in and out of plants, secretory glans, various hairs, cells in
which crystals are isolated and other that greatly increase absorptive
parts of roots.
* see page 57 for diagrams
Xylem conducts “raw” sap – water and minerals – from the roots to the leaves, where
Tracheary elements: Tracheids are primitive;
dead, ± elongated cells with thinner and longer
cell wall very thickened
with lignin. Although dead,
they are still capable to Vessel
fulfill their role of members are more evolved;
conducting water and shorter and wider
minerals absorbed by the
important for transport function. It is also important for support of structure of the plant. Two different kinds of Tracheary elements:
Tracheids Vessel Members
V.m. have larger openings called
Tr. have perforation plates on their endwalls.
overlapping V.m connect longitudinally to form
end walls vessels, 10 cm to a few meters long!
through pits More evolved because they are
derived and more efficient for
Xylem tissue important component of the “plumbing” and storage systems of a plant and
is the chief conducting tissue throughout all organs for water and minerals absorbed by
Consists of a combination of Parenchyma cells, fibers, vessels tracheids, and ray cells.
Vessels are long tubes composed of individual cells called VESSEL ELEMENTS, which
are open at each end. TRACHEIDS: are dead at maturity and have relatively thick secondary cell walls, are
tapered at each end, the ends overlapping with those of other tracheids.
Have no opening, but are usually pairs of pits present wherever two tracheids are in
contact with one another.
Pits are areas in which no secondary wall material has been deposited, they allow water
to pass from cell to cell.
In conebearing trees and certain other nonflowering plants, the xylem is
composed almost entirely of tracheids.
Most conduction through xylem is upward, but some is lateral(sideways).
Lateral conduction takes place in the rays.
Ray cells, which also function in food storage, are longlived parenchyma cells
that are produced in horizontal rows by special ray initials of the vascular
Inside both vessels and tracheids, there are additional lignin thickenings. This slows the
fluid going thro