Fertilization

In some plants, one of the Synergids starts to die. It must release some chemotactic agent as the pollen tube is attracted to it. The Pollen Tube grows through the Micropyle & may enter the senescent synergid. The pollen tube wall degrades and the sperm are released.

The Egg and the Central Cell have incomplete cell walls & the sperm has no wall. One Sperm enters the Egg while the other enters the Central Cell.

The Zygote is formed when a Sperm nucleus fuses with the egg nucleus (Syngamy). This will develop into the Diploid Embryo.

The Endosperm is formed by the fusion of a sperm nucleus with the nuclei of the Central Cell. It is therefore Polyploid (3N). The Endosperm surrounds the developing embryo and provides a source of nutrition for the Embryo during its differentiation and seed Germination. Thus, Double Fertilization occurs!

Syngamy

Embryogenesis - General & Lilium (monocot)

The early embryo develops into a tubular, three dimensional structure in Monocots and Dicots. Lilium is the model for monocot embryogenesis. Capsella is used for dicots.

Both have a Suspensor. Dicots have a suspensor that is a unicellular filament, while Monocots have suspensors which are several cells in width.

In both cases, the Suspensor is minute compared to the Embryo.

In some plants, like coconut palm the embryo is very small and is surrounded with a large endosperm. Coconut Milk is liquid endosperm and the "meat" is solid endosperm. The endosperm is consumed during seed germination.

In other plants the endosperm becomes completely cellular early in development and may be consumed by the embryo. Nutrients absorbed by such embryos are stored in their Cotyledons.

As you might suspect, some species are intermediate in terms of endosperm development.

Early stage in Lily Embryogenesis. note the Nuclei in the periphery of the Endosperm. Cellularization has started but most of the Endosperm is liquid.

Lily Embryo Showing the Suspensor.

Mature Lily Embryo. Note that the Embryo is small and undifferentiated. Organ formation is delayed until germination.

The Lily Embryo is relatively undeveloped at this point.

Further growth of the embryo leads to the formation of an asymmetric embryo that has a broad apex.

A Lateral Meristematic region becomes apparent. This marks the site where the Root-Shoot axis will develop.
The area above this will produce the Cotyledon.

Mid-Stage Model of a Monocot Embryo - Note the Notch where the lateral origin of the Root-Shoot Axis occurs.

Saggitaria Seed with a Mature Embryo. This is a Monocot because it has only one Cotyledon. The Shoot Apical meriastem (SAM) has a Lateral position. The Root Apical Meristem (RAM) is directly opposite to the SAM. Note the Seed Coat which develops from the Integuments. Amyloplasts are prominent in all of the Embryo's Cells. The Endosperm is not prominent. Consequently this seed is Exalbuminous! The Seed is surrounded by the Ovary Wall (Pericarp).

Double Fertilization

In some plants, one of the Synergids starts to die. It must release some chemotactic agent as the pollen tube is attracted to it. The Pollen Tube grows through the Micropyle & may enter the senescent synergid. The pollen tube wall degrades and the sperm are released.

Embryogenesis - General & Lilium (monocot)

The Lily Embryo is relatively undeveloped at this point.

Further growth of the embryo leads to the formation of an asymmetric embryo that has a broad apex. A Lateral Meristematic region becomes apparent. This marks the site where the Root-Shoot axis will develop. The area above this will produce the Cotyledon.

Further growth of the embryo leads to the formation of an asymmetric embryo that has a broad apex.

A Lateral Meristematic region becomes apparent. This marks the site where the Root-Shoot axis will develop.
The area above this will produce the Cotyledon.