Botany and Plant Science

Xenia in plants is the effect of pollen on seeds and fruit of the fertilised plant. The effect is different from the contribution of the pollen towards the next generation. The effect, such as an increase in size, on the embryo or endosperm of a plant results from fertilisation with pollen of a genetically distinct variety.

Tree rings grow under the bark and the bark is pushed out while the tree is growing. The inner part of a growth ring is formed early in the growing season, when growth is fast, and is known as early wood. The outer portion is the late wood, and is denser than early wood. This is formed by the activity of intrastelar cambium and interstelar cambium.

Stamens are fused together, at least partly, by the filaments so that they form two separate bundles. This is the characteristic of family Fabaceae.

Angiosperms form fruit. Gymnosperms, being the naked seeded trees, do not form a fruit.

Sieve tubes are connected with perforated sieve plates. They help in the conduction of food downhill.

A meristem is the tissue in most plants that contains undifferentiated cells (meristematic cells). It is found in zones of the plant where growth can take place. Meristematic cells give rise to various organs of the plant and keep the plant growing.

The response of an organism or its part is termed 'positive' if the growth is towards the stimulus or 'negative' if the growth is away from the stimulus. An example of chemotropic movement can be seen during the growth of the pollen tube, where growth is always towards the ovules.

Stigma serves as the receptive structure for pollens.

Chemotactic movement is performed by pollen tube towards embryo sac.

A pollen tube usually enters the embryo sac through one of the synergids.

This is the characteristic of angiosperms, and not gymnosperms. Here, the xylem is made up of xylem parenchyma, tracheids and fibres only.

There are two forms of polyembryony with respect to the origin of the embryos: simple, due to the fertilisation of several eggs and cleavage, and due to the splitting of products of zygote. This is common in pinus.

Each microsporophyll has two attached microsporangia. Microsporangia are organs that contain microsporocytes (immature pollen grains).

Duramen is the name given by botanists to the central wood or heart wood in a tree trunk.

Pollination in Cycas occurs at three celled stage (prothalial cell, generative cell and a tube cell).