Aestivation and Placentation

Aestivation

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Mode of an arrangement of sepals or petals in the bud is known as aestivation. It is of different types, they are:

Valvate

In this type, the sepals or petals are arranged in the same circle without overlapping each other.

Twisted

In this type, one end of the member is overlapped and its another end overlaps the third member i.e. the members are arranged in alternately in and out the pattern.

Imbricate:

In this case out of five members, one is completely in, one member is completely out and remaining three members show the twisted pattern of arrangement.

Quincuncial:

It is a special type of imbricate aestivation in which out and of five members, two are completely out, two are completely in and remaining one member shows the twisted type of arrangement.

Vexillary:

This type of aestivation is seen in petals only. Here the posterior largest petal known as standard or vexillum partially or completely covers the two lateral medium sized petals known as wings or alae which completely overlap the two anterior small fused petals known as keels or Carina.

Placentation

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The placenta is the tissue through which ovules remain attached to the ovary wall and get nutrition. Mode of the arrangement of placenta inside the ovary is known as placentation. It is of different types they are:

Marginal:

The ovary is unilocular and placenta arises along the margin of two sutures of an ovary. Eg; pea

Parietal:

The ovary is unilocular or sometimes bilocular due to the false septum and the placenta arise around the inner wall of the ovary. Eg; Brassica

Axile:

The ovary is bilocular to multilocular with distinct septa and the placenta arise directly from the central axis. Eg; Tomato

Central:

It is same as axile but without distinct septa.

Basal:

The ovary is unilocular and placenta arises from the base of ovary. Eg; Tagetes