Over time the seed plants became more sophisticated.
Some Gymnosperms probably those of the Gnetophytes, a sister branch to the conifers, started to protect thier ovules in a carpel.
The ovule or ovules and carpel together make the ovary.
For pollen grains to have access to the ovules and the female gametophyte (egg) within, a special place for the pollen to land was developed.
This is called the stigma and is usually atop of a style (tube to the ovary).
While the seed plants were doing all this they were also developing a relationship with animals, mostly insects, to help in pollination.
Having insects carry the pollen from the anthers (male) of one flower to the stigma (female) of another, the plant does not need to produce nearly as much pollen as it would if it relied on wind pollination.
Flowers also developed bisexuality.
They have both male and female parts in the same flower.
Some species though have what is called imperfect flowers of only one gender, male or female.
The first angiosperms (flowering seed plants) appeared only 140 MYA but now account for 96% of all vascular plant species.
For more flower terms and diagrams visit the Flower Glossary Page.
For the most part flowers are showy (colourful and relatively large petaled) as they are intended to attract pollinators.
Most plants attract insects as pollinators and some are very specific as to which sort of insect (flying or walking).
Some are even specialized to attract a specific species.
Other flowers may be pollinated by birds or mammals.
Some flowers are not showy at all and rely on different means of getting thier pollen to a flower pistil.
Some families such as those bearing catkins and the graminoids (grass like species) do not have showy flowers at all. They have reverted to wind pollination.
Others such as some aquatic species also lack showy flowers and rely on water to distribute thier pollen.
It should be noted that pollination is simply the moving of a pollen grain from an anther (male) to a stigma (female) of another flower or the same flower.
It is not the same as fertilization,the joining of the male and female gametes, which happens after pollination if everything goes well.
A fruit is formed when a flower is fertilized.
It is the product of the changes in the flowers ovary.
Fuits are so varied that it is difficult to come up with a simple classification scheme.
Botanists have developed a vocabulary of over 150 fruit terms in thier efforts.
Many fruits are flase fruits such as juniper berries which are actually fleashy cones or strawberries which are not produced from the ovary and so not technically a fruit.
There are three basic types of fruits:
- A simple fruit is one where one flower with one pistil makes one fruit.
- A aggregate fruit is one where one flower with many pistils makes a fruit with fruitlets.
- A multiple fruit is the product of an entire raceme (group) of flowers makeing a fruit with numerous fruitlets.
There are also three basic categories of fruit classification:
- Ovary type: apocarpous (1 ovule) or synocarpous (2 or more ovules)
- Fruit wall: soft/fleashy or hard/dry
- Fruit opens at maturity or not: dihiscent (opens) or indihiscent (not opening)
- Mature sporophyte produces pollen (male) and egg (female) in the flower.
- Pollination occurs when the pollen is transported by insect, wind, water or otherwise to the stigma (female, pollen receptor).
- The female gametophyte (egg + related tissue) grows inside the ovule.
- The male gametophyte occurs in the form of a pollen grain germinating on the stigma. The pollen grain starts developing a tube that grows down into the ovary and into the ovule to the macrogametophyte (female).
- Fertilization then occurs by 2 male gametes (sperm) delivered by the pollen tube directly to the macrogametophyte.
- Angiosperms have double fertilization. One sperm feritilizes the egg creating a zygote. The other joins with special cells of the macrogametophyte.
- The special cells then start to divide very rapidly creating a very nutritious tissiue called endosperm.
- The zygote grows into a sporophyte embryo useing the endosperm as food.
- At the same time the pericarp (ovary walls) start to develope in to a fruit, while the ovule walls become the sead coat.
- At the end of this process a seed has been created.
- An angiosperm seed consists of a plant embryo with nutritious endosperm in a seed coat inside a fruit.
- The seed is then dispersed by one of a number of means such as: mammals, birds, insects, water, wind, gravity or ejection.
- When conditions are right, the seed will germinate giving rise to a new sprophyte plant.