Question

In distichous condition,
a. First leaf stands over the second
b. Second leaf stands over the first
c. Third leaf stands over the first
d. Fourth leaf stands over the first

Answer 1

Hint: Phyllotaxy the arrangement of leaves on the stem, it is the Greek word where phyllo indicates the leaves and the taxy indicates the arrangement, The term phyllotaxy was coined by the scientist Charles Bonnet.

Complete answer:
Basically, the arrangement of leaves is classified into the following types.
> Opposite: The leaves are arranged in such a way that they are opposite to each other at the internode. Example is calotropis.
Again this opposite into divide into two categories they are:
- Opposite and decussate: It is when two pairs of leaves that are arranged at right to each other come under this category example is psidium.
- Opposite and superposed: when all the leaves on the plant have occurred from the same plane example is combretum.

> Alternate: when only one leaf develops at each node and it is called an alternate type of phyllotaxy, where the example includes Brassica and Nicotiana and hibiscus.
They are again categorized into the following types:
- Distichous: If a third leaf comes over the first it is called as distichous or half or two ranked examples are grasses.
- Tristichous: if a fourth leaf comes over the first one and example is grasses.
- Pentastichous: when 6th leaf comes over the first leaf after two revolutions of spirals and example is apple.
- Octastichous: when the 9th leaf comes over the first leaf after three revolutions of spirals and example is Carica papaya.

> Whorled: when more than two leaves are arranged in the form of whorl at each node is called as whorled phyllotaxy and examples are Hydrilla, Nerium, Allamandha, etc

Hence, the correct answer is option (C).

Note: The aim of the phyllotaxy is to avoid crowding of the leaves and to expose the leaves properly. And examples of each phyllotaxy are important, as it is different in different plants, based on the habitat area, and based on adaptations.