Download GHf12 Lab 2 Sexual Reproduction

General Horticulture
Plant Reproduction with Seeds
Laboratory 2
Seeds
Seeds are the means of sexual reproduction in the higher plants. When pollen lands on the
stigma portion of the reproductive structure in the seed plants (pollination), a pollen tube grows
down to the ovary and allows for sperm to join with the egg within the ovary. The structure
within the ovary where this takes place is called the ovule. The fertilized and mature ovule is the
seed. Of course, the reality is a bit more complicated than this, but this is the essential summary.
In this laboratory you will become more familiar with seeds. We will examine several kinds of
seeds with the naked eye and with magnification.
Bean seeds
First examine the dry bean seeds and note the hardness. Next, inspect the soaked seeds and
carefully peel off the seed coat. You will then be able to examine the seed cost, cotyledons, and
the embryo. If you look carefully you will be able to see the radicle and the very young leaves.
Make appropriate drawings (photos are okay too).
In addition to various been seeds, we also have some dry peanuts in the shells. Break these apart
and compare with the other seeds. I would like you to investigate the so-called Sunflower seeds
too. In addition, I want you to look at the olives and the dates. Take the time to look at the green
beans and tomatoes that are on display.
We have red, kidney beans, small white bean, and lima beans for you to examine. Are there any
significant differences between these that you can see?
All of these bean-type seeds are legumes (Fabaceae). The legume family is one of the most
important plant families and you should know a little bit about them. Legumes are nitrogen
fixers; as such, they take nitrogen gas from the atmosphere that is unavailable for plant nutrition
and convert it to a form that is available to plants (more on that in lecture later). The legumes do
not actually do the conversion; inside the roots are nodules containing bacteria that actually do
the conversion from gaseous nitrogen to a form of nitrogen that the plant’s roots can take up and
use. As you are probably thinking, these plants must be very important in agriculture and in
natural systems. If that is what you were thinking, you are correct! This is a plant family with
lots of species and in the tropics there are many, many are trees. In the temperate zones the
family is better represented by herbs. Beans are also one of the most important sources of
(c) 2012 John H. Crow, Ph.D., all rights reserved
General Horticulture
Page 2
protein and essential amino acids in the human diet. If you happen to be a vegetarian, legumes
are absolutely critical to you.
We do have a few legume tree species in our region that belong to this family. Perhaps the most
important is the Black Locust but there are some others too. Of course, in the vegetable garden
we grow quite a few kinds of beans to eat. The same can be said of agriculture with the addition
of alfalfa which is grown for animals to eat and because it is a good nitrogen fixer. You have
undoubtedly heard of clover, that is also a legume. We enjoy honey from clover, so the legumes
are important in lots of ways. We should not forget the garden plants such as lupines and sweet
peas either. Professor Crow will show you some of these in lecture and we may see some in lab
later.
For the best luck with germinating the bean seeds you grow at home, there is a benefit from
some soaking the seeds prior to planting the seeds. You have already found that the soaked seeds
are softer and usually germinate better.
Corn
Take a look at the ear of corn in front of you. What you think is a seed is actually a fruit, and
there are lots of them on a single ear of corn. This kind of fruit is known as a grain or caryopsis.
As before, examine dry, fresh, or soaked “seeds” and make observations.
First of all, can you even find the seed inside? It is not easy but you may be able see it better
with the soaked material. You will probably have to use forceps, a needle or two, and a razor
blade or small knife. If you are lucky you will see that the seed is fused to the wall of the fruit
(ovary) and has only one cotyledon. As you can see, this is not as simple as was the situation
with the beans. We should note that the flowering plants with only one cotyledon are distinctly
different from the flowering plants with 2 cotyledons; the former at known as the Monocots and
latter are the Dicots.
Obviously corn is important in agriculture and in large vegetable gardens. A small vegetable
garden is probably not the place to grow corn very productively but it can still be fun (ask Dr.
Crow why this is so).
Corn is native to the Americas and was not found elsewhere in the world before the discovery of
America. Corn is now grown around the world and is one of the big three crops along with
wheat and rice. All three of these great crops are grains and they account for most of the calories
and protein grown in agriculture for food.
If you are a vegetarian you can eat a legume and a grain and get all the essential amino acids. Of
course, you can also just eat any meat or fish to get all the essential amino acids. Have you heard
of the Italian soup known as Pasta e Fagioli or just Pasta Fagioli for short? This is pasta
(c) 2012 John H. Crow, Ph.D., all rights reserved
General Horticulture
Page 3
derived from a grain and the bean, Phaseolus vulgaris in a meatless soup. Just about every
country has some kind of equivalent where a grain and a legume are put together to provide all
the essential amino acids. This combination is very important in the diets of poor people around
the world and has also become part of the traditional foods on the menus for all to enjoy. Oddly,
the Phaseolus bean for which the soup is, in part, named, was now known from the old world
prior to the discovery of the Americas. So, this Italian soup is named for an American plant!
Other seeds
A variety of other seeds will be available for study. Make appropriate notes and sketches.
Compare the seeds. Look at the sizes of the seeds. Investigate and make some notes. It is
amazing how the tiny seeds contain the critical parts seen in the larger seeds. I am going to have
you take some home and germinate a few. You will want to use the dissecting scope for some of
your observations
Starting seeds
A variety of seeds, media for starting seeds, and small pots will be available for you to work on.
You lab instructor (Prof. Crow) will demonstrate to get you started. What are the materials you
can use for germinating seeds. What would you do outdoors? How do you control mold? How
do you keep the seed from drying out.
It is always important to start (and plant) seeds in a medium that will easily supply water and air.
Also, we are especially concerned when the seeds are tiny. For tiny seeds a really coarse starting
mix is not best but one that is very fine has to be managed carefully ... and that is part of the fun
of horticulture. How deeply should the seeds be placed?
We want you to plant a few seeds and manage the seeds through germination and, of course,
beyond. The seeds should come up pretty quickly. In some instance you will have to transplant
the seedlings or small plants to another pot. While we are at it, what is a seedling? By the way,
you may need to transfer the seedlings to another pot later on. Lets see how large and good
looking the plants will be by the end of the semester and what luck you have growing them.
Other
Continue any any lab work with available materials that was not finished last week.
(c) 2012 John H. Crow, Ph.D., all rights reserved