Fertilisation & Germination

Fertilisation in Plants

Concluding Plant Reproduction

Plant fertilisation When pollen sticks

to the stigma it absorbs water and starts to germinate

A pollen tube will grow out of the grain and through the style towards the ovary

Plant fertilisation The pollen tube

nucleus remains close to the tip of the tube.

Digestive enzymes are secreted from the tube.

The tube is attracted by chemicals given out by the ovary.

Plant fertilisation As the tube grows

the generative nucleus divides by mitosis to form two haploid male gametes.

Plant fertilisation The pollen tube enters

the ovule through the micropyle.

Once inside the ovule the tube nucleus degenerates and the male gametes enter the embryo sac

Plant fertilisation One of the male gametes fuses with the

female gamete forming a diploid zygote. In plants a double fertilisation takes place

as the other male gamete fuses with the diploid nucleus in the centre of the embryo sac forming a triploid nucleus – called the endosperm nucleus.

Outbreeding mechanisms

How plants prevent self-fertilisation

Protandry Most flowers use

this mechanisms, e.g. rose-bay willowherb

The stamens ripen before the stigma is receptive to pollen.

So pollen is gone by the time stigma is ready.

Protogyny More unusual than

protandry e.g. the bluebell

The stigma ripens before the anthers.

By the time the anthers shed their pollen the stigma is no longer receptive to it.

Dioecious Plants With dioecious

plants each individual plant bears either male or female flowers, but never both.

Dioecious Plants Paw-paw and holly

are examples of dioecious plants.

Clearly self-pollination is impossible!