Question

Cycas stems shows
A. Porous wood
B. Manoxylic wood
C. Pycnoxylic wood
D. Ring porous wood

Answer 1

Hint: Cycas, a genus consisting of 105 species of tropical and subtropical ornamental palm-like cycads (the Cycadaceae family), including trees 12 metres (40 feet) or more in height.

Complete Answer:
Gymnosperms are plants that grow naked seeds, i.e., plants that do not produce fruit without ovaries. This community of plants belongs to Cycas. Because of the presence of several recurrent leaf bases, the stem is irregular in outline. Its inner structure is identical to that of Angiosperm dicots. The epidermis, cortex and vascular cylinder are divided into young cycas stems.

Epidermis:
- The outermost layer of the stem is bound by a dense cuticle. The bulk of the stem forms the cortex.
- It consists of cells with rich starch grains that are parenchymatous. Several mucilaginous canals and several fragments of leaves traverse the cortex. The pericycle-followered endodermis is the innermost layer of the cortex.
- Compared to the cortical zone, the vascular region in the young stem is very small. In a ring, multiple vascular bundles are arranged.
- Conjoint, collateral, endarch and open are the vascular bundles. Parenchymatous medullary rays separate the individual bundles. Tracheids and parenchyma are made of xylem. Vessels from Xylem are absent. The phloem consists of phloem parenchyma and sieve tubes. The companion cells are not there.
- In the centre of the stem is a parenchymatous pith current. Pith cells are rich in starch, and tannin and mucilaginous substances are present in certain cells.
- Secondary development, i.e. the formation, as seen in dicot stems, of secondary xylem and secondary phloem from cambium, is observed in old cycad stems.
- The cambium also develops parenchymatous medullary rays in addition to secondary xylem and secondary phloem. A well-developed cycas stem is called manoxylic since, due to well-developed pith, cortex and large medullary rays with minimal vasculature, the wood is not compact.

The correct answer is option (B) Manoxylic wood.

Note: Cycas species are of great economic significance. Starch is derived from a variety of cycas species. Young, succulent leaves are used in some parts of India as vegetables. Many species of cycas are of medicinal significance. As a treatment for gastrointestinal disorders, flatulence, blood vomiting and skin diseases, juice from young leaves of Cycas circinalis is used.