Question

Describe the internal structure of the leaflet of cycas and list out the xerophytic adaptations seen in it.

Answer 1

The leaflets in the plant of cycas are termed as pinnule. There is upper and lower epidermis which have the compactly arranged cells and below is the layer of the hypodermis. There are stomata on the upper and lower epidermis. The mesophyll is divided in two tissues, palisade and the spongy tissue. The palisade tissue contains long cells which are arranged compactly. There is spongy tissue which has the loosely arranged cells. The vascular bundles are conjoint and collateral. The protoxylem is towards the lower epidermis and the metaxylem is towards the upper epidermis. The xylem is central and centrifugal in the arrangement. There is phloem tissue arranged near the lower epidermis.

There are certain adaptations in these plants similar to the xerophytic plants. There is a thick cuticle which protects from excessive transpiration. There are sunken stomata which reduce the loss of water. There are certain thick walled cells of hypodermis which does not allows the passage of water and prevents water loss. The last leaflets are modified to form the spines which reduce the surface area for transpiration.