Question

In which of the following is an excurrent stem found?
(A) Cycas
(B) Pinus
(C) Mango
(D) Wheat

Answer 1

Hint: The current stem is found in conifer which comes under the family Pinaceae and the sole genus in the subfamily Pinoideae. Due to this type of stem present, plants take pyramids or cones like shapes.

Complete step by step answer:
Excurrent stem found in the plant Pinus. An excurrent stem is the sort of stem within which the main stem grows indefinitely. The side branch grows in an acropetal manner in which old flowers are arranged in the lower side and young flowers are at the upper side. The main stem in this type of plant is trunk-like. It's thickest at the bottom and gradually tapers towards the apex.

So, the correct answer is ‘Pinus’.

Additional Information: A stem develops from the plumule and epicotyl of the embryo and is an ascending axis of the plant. It's generally erect and grows faraway from the soil towards the light. Therefore, it's negatively geotropic and positively phototropic. There are different types of stems seen. They're as follows:
- Reduced stems: In some plants, the stem is in the kind of a reduced small disc which isn't differentiated into nodes and internodes. e.g. fleshy roots of Radish, Carrot, and Turnip.
- Erect stems: The majority of angiosperms possess upright, vertically-erect stems. Erect stems belong to four categories :
- Culm: Erect stems with solid nodes and have hollow internodes. The nodes are swollen giving the stem a jointed appearance e.g., wheat.
- Caudex: In this, the main stem remains unbranched and bears a crown of leaves at its top. e.g., Coconut, etc.
- Excurrent: An excurrent stem is the sort of stem within which the main stem grows indefinitely.
- Decurrent or Deliquescent: In this, the main stem grows up to a particular height after which it gives several branches. The entire tree seems dome- shaped. e.g., Banyan.
- Weak stems: they're thin, soft, and delicate which are unable to remain upright without any external support.

Note: In manly plants, it is seen that stem is modified into different shapes and structures and also performs different functions. For example:
- Underground Stem. They help in storing plenty of food material. Examples include rhizome of banana, bulb of onion, and corm of Colocasia.
- Aerial Stem: The aerial stems show many modifications. For example tendrils of grapevine, the thorn of citrus fruit plants, and many more.