Reproduction

Maple seeds

All reproduction serves two purposes. Firstly it increases the number of individuals of a particular species, thus providing a larger gene pool for the naturally occurring genetic changes. These changes enable species to cope with and take advantage of new, or changing environments. This process will often result in the evolution of a new species. Secondly it provides a food source for predatory, or parasitic species.

The higher plants usually reproduce sexually, with the joining of the sets of the parent plant's genes one of the main occasions for the genetic change to occur. However sexual reproduction is not the only way plants propagate, or can be propagated as we shall see.


Trees are divided into two types, Gymnosperms, the conifers, and Angiosperms, the broadleaved trees. They are classified by the covering (or lack of) of their seeds.

An Angiosperm a Peach and a Gymnosperm a Pine


Mosses, Liverworts, Fungi and Ferns do not produce flowers and seed, but rely instead on 'spoors'. These spoors are self-fertile and are often small enough to be carried on the wind.

The higher plants have flowers, with both male and female parts to distribute their genetic code and produce seed. Unusually however some trees, Pines being an example, have the male and female reproductive parts on separate flowers, often carried on different branches.

An Angiosperm flower

A typical Angiosperm flower consists of the male, pollen-producing stamen. The female pollen receptors, the stigma and the seed producing ovary.

The petals are really only there to attract pollen eating and of course distributing insects.

The fruit that develops around seeds serves two purposes. Firstly it proves attractive to fruit eating animals and birds, the seeds are generally resistant to the gastric juices of both and will pass out of the diner, pre packaged in its own little pile of compost.

If the fruit should, perhaps as a windfall, end up on the ground, it is yet again surrounded by its own compost heap.


Fertilisation may be carried out by a number of agents. Insects, particularly bees are the best known pollinators, however birds, wind and some animals such as fruit eating bats also play their part.

The pollen is carried from stamen of one flower to the stigmas of another. To avoid self-fertilisation most plants have the stigma and stamen mature at different times.

On reaching the stigmas, the pollen is transported down the tube they are mounted on, to join with the female seed, fertilising it.

An Angiosperm flower


Female and male Gymnosperm flowers

Gymnosperms, the conifers differ in that flowers are either male, pollen producing, or female, seed producing.

The female flower will develop into the cone, the male will drop off after shedding its pollen.

The pollen of Gymnosperms is usually distributed by wind and anyone who has been in a pine forest at pollen time will be familiar with the clouds of yellow, dust like pollen.


Not all gymnosperms have cones. Some such as the Yew and Ginkgo have fleshy covered seeds called 'arils'.

The friut of a yew tree, enclosing the seed


Most non fruiting trees rely on the wind to distribute their seeds, often over long distances.

A popular way of keeping the seed in the air to cover greater distances, is with a wing like structure, as with Pine, or Maple seeds.

Pine seeds are carried in pairs, on each of the cones segments.


A raft style tree

We are able to force the issue of tree reproduction by creating new trees from cuttings, or by layering a tree. Certainly layerings occur naturally, As branches mature they get heavier, this weight will often cause them to touch the ground. Prolonged contact with the ground will cause roots to develop, creating what we in bonsai call a 'Raft' style tree.

The parent tree may eventually die but the rooted layering will go on and live out its natural life span, of perhaps several hundred years.


Another way that plants reproduce is to produce 'suckers'. These grow from adventitious buds that develop on the roots.

These suckers will grow on to be mature trees.

Cuttings, layerings and suckers are asexually reproduced and hence carry only the genes of the plant they were taken from. The advantage of this in bonsai is that asexually produced trees, when planted in a group all exhibit the same growth characteristics such as leaf colour and size.


Ferns,Fungi, Moss and Liverworts

Fungi are plants that feed on other plants. They reproduce by means of 'spoors', small (microscopic) seeds which are distributed by the wind, or water. Should a spoor be able to enter your plant, perhaps through a cut or other wound, it will begin the process of breaking down the tissue, killing the plant. Modern fungicides will get rid of an established fungus, but often, by the time you notice the fungus, the damage is done. They are best used to prevent fungi from becoming established, or to control their spread. Fungi are quite common in all kinds of gardens and especially with fruit plants, which need to be sprayed routinely.

Here we see a 'Bracket' fungus on a beech tree. The red dust is the spoors.


Ferns carry their spoors in rows under the leaves.


Liverwort

Liverwort is a primitive plant, one of the first land dwelling plants to evolve. It's ususlly found in poorly drained pot plants. The plant reproduces in two ways. Firstly it has a small umbrella like growth, that produces spoors, pick these off as soon as you see them.

Secondly on the flat plates that make up the plant you will see cups, each of which contains gammae, small plantlets that, if splashed out of the cup by rain, or watering, will develop into new plants. Dabbing the liverwort with malt vinegar will kill it and any spoors in the area, however you should bear in mind that vinegar is acidic, so don't overdo it.

A Liverwort, showing the 'cups'


Allen. C. Roffey 11:30 11/02/2003