Understanding Basic Seed Saving Botany Sounds Tedious But Is Important If We Are To Save Seed. It’s Not Difficult As This Article Demonstrates.
The Facts Of Life For Plants
If we want to learn how to collect seeds from vegetables we need to understand the basic vegetable plant botany. Let’s start with the most basic fact. To produce seed we need both males and females. That might seem obvious but plants don’t always make their gender obvious. In this article we wil look a this and other Basic Seed Saving Botany.
For example peas are quite straight forward and have both male and female parts on the same plants. They are in the same flower. It’s the same with tomatoes, both male and female parts are in each flower.
Then we have plants such as squashes .. that includes marrows and courgettes .. where w have both male and female parts on the same plant. But this time there are separate male and female flowers. And they don’t always flower at the same time. To make this slightly more difficult some plants such as cucumbers cane have both male and female flowers on the same plant but plant breeders have produced some all female plants. All female cucumbers are something I love from a growing perspective as there are no pollination issues.
Botanists describe the above types of flowers as follows ..
- Perfect Flowers. They contain both male and female reproductive organs.
- Imperfect Flowers. These are flowers that are either male or female but not both at once
- Monoecious Flowers describe those where both male and female flowers grow on the same plant
- Dioecious Flowers are found on separate plants. There are both male and female plants.
The trick in producing seed is simple. We need to male and female plants to come together to form seed.
Plant Reproductive Parts
Plant parts have botanical names that it’s good to know. It makes it easier to understand the instructions when we describe how to pollinate flowers.
Female Flower Reproductive Parts
The female reproductive parts of the are called the pistil. It consists of a stigma, style and ovary.
The ovary is where the seed forms and can contain one of more sections (ovules)for the seed to form in.
The stigma is the part that collects the pollen from the male and is sometimes sticky so the pollen doesn’t escape! In many flowers the stigma is small and hidden deep in the flower. But in some crops it is very obvious. In maize the stigma are the long silken tassels we see as the cob forms. they collect wind blown pollen so have to be obvious and capable of collecting enough pollen to fertilise each maize grain.
Male Flower Reproductive Parts
The male reproductive part in the flower is called stamen. Some flowers only have one stamen and some have many stamen. The number of stamen in a flower is what botanists use to help them identify plants.
Each stamen consists of a filament (it’s bit like a stalk). On the end of the filament is the anther. The anther produces the pollen and is held aloft by the filament so that insects and even the wind can access the pollen.
The Flower Pollination Process
For fertilisation to take place a fertile pollen grain needs to land on a receptive stigma. Then the pollen needs too grow a tube that reaches the ovary so that ti can fertilise one of the ovules. After that the ovules develop to form seeds. The ovary will then turn into a fruit or seed pod depending on the type of plant.
Plants That Don’t Need Pollination
Parthenocarpic plants don’t need pollination but produce seeds without going through the above process.
Flower & Seed Purity
Both the pollen and ovules contribute genetic material to the developing seed . And we know from the work of Gregor Mendel and others that the genes get shuffled so that each seed is slightly different. It’s the same with animals and even people. Even with the same parents we are all slightly different.
Though there is a shuffling of genes we want to keep the same sort of genetic material in the seed sas in the plants we collect seed from. That is not problem provided we there is no cross breeding. But think what happens when we breed two sorts of dogs, pigs or cattle together. If they are different breeds we end up with offspring that have some of the characteristics of the parents but aren’t actually like either of them. So it is with seeds. If seeds cross breed they will produce a mongrel offspring that is neither one thing or another. Mongrel dogs maybe loveable but they aren’t purebred. When plants aren’t purebred they tend to exhibit all sorts of undesirable traits such as bitter fruit or tough skins.
So, as seed savers, we need to ensure our plants aren’t cross bred and are as pure as they can be.
More on Perfect Flowers & Basic Seed Saving Botany
Where we have perfect flowers, those with both male and female contained in one flower, it’s easy. They tend to self pollinate and very rarely do they cross pollinate. In many cases even if bees tried the pollinate them they couldn’t because the flower is the wrong shape.
Peas are perfect flowers and they have taken the process a stage further. They are cleistogamous. Cleistogamy is Greek and means closed marriage. Cleistgamous flowers are fertilised before they open.
Tomatoes flowers are also perfect, but they are not cleistogamous. But they do need special conditions. For the pollen to move from the anther to the stigma it need a gentle nudge. If the flowers vibrate in the breeze its enough to dislodge the pollen. In a greenhouse or polytunnel there are fewer breezes so w need to help the pollen to dislodge. I often see people suggest using a fine paint brush or a rabbits tail, but they aren’t needed. On my nursery we used a jet of cold water straight from a hosepipe to move the plants in the greenhouses. It was enough to dislodge the pollen. And the water raised the humidity. Tomatoes need a certain level of humidity for the pollen to germinate and reach the ovule. If the air is too dry then fertilisation fails.
In very wet weather we didn’t want to increase the humidity too high so we either walked up and down the rows of tomatoes and brushed them enough to dislodge the pollen. An alternative was to use a motorised high volume fan which acted like a fierce wind and moved the plants.
Non Compatible Flowers
Some species of plant are not self compatible. They need another tree to pollinate them. this is often the case in fruit trees such as apples. Apples are arranged into flowering groups and many require an apple from another group to pollinate them. Non compatibility isn’t an issue for most vegetables as they have evolved to overcome this.
Vegetable Pollination Vectors
Where a plant doesn’t have perfect flowers the pollen is transferred by insects such bees, other insects, or the wind.
Fine pollen can travel miles on the wind so crops can cross pollinate with plants from miles away.
To prevent promiscuous cross pollination flowers can be protected in cages, or be bagged.
A Seed Oddity
Most seeds are easy to harvest as they are found in the fruit or pods that hang from the plant. Peanuts break that rule. Peanuts are geocarpic. Geopcarpic plants do something strange after pollination. They force the flower into the soil and the seed develops underground.
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