Question

Phyllotaxy is:
A. Arrangement of young leaves in bud
B. Arrangement of mature leaves on branches
C. Arrangement of branches
D. Arrangement of floral leaves in a floral bud

Answer 1

Hint: Leaves borne by the stem show a definite arrangement. It varies from species to species and sometimes even on different parts of the same plant. Leaves show three vital functions, photosynthesis, exchange of gases and transpiration.

Complete answer:
Phyllotaxy is the arrangement of leaves on branches. The basic principle is to allow leaves to receive sufficient light for photosynthesis. Three principal types of phyllotaxy is noticed in plants are:
1. Alternate- It is also called spiral phyllotaxy. In this type only a single leaf arises at each node in an alternate manner. If a string is passed around the stem along the bases of successive leaves at consecutive nodes, spirals would be formed. This is called a genetic spiral. Example- Mustard, China rose, Sunflower.
2. Opposite- In this type, two leaves occur at each node standing opposite to each other. On the basis of relative position of leaves on adjacent nodes, opposite phyllotaxy may be of following two types:
a) Opposite superposed- The pair of leaves at one node stands directly over the lower pair. In this type, if the stem is viewed from above only two leaves are seen. Eg. Guava.
b) Opposite decussate- The leaves at each node are at right angles to the next pair, above or below. Such a stem when viewed from top shows four leaves. Eg. Calotropis.
3. Whorled- In this type, if more than two leaves arise at each node which are arranged in a circle or whorl. Eg. Alstonia, Nerium.

So, the correct answer is ' arrangement of mature leaves on branches'.

Note:
All the leaves in alternate phyllotaxy seem to appear to be arranged in a fixed number of vertical rows called Orthostichies.
In alternate phyllotaxy, on the basis of number of leaves in relation to spirals, it is classified as- Distichous (leaves are arranged in two vertical rows), Tristichous (leaves are arranged in three vertical rows forming a spiral), Pentastichous (leaves are arranged along five vertical rows).
In whorled phyllotaxy, Alstonia is also called Devil’s tree.