EXPERIMENT 7.2 Objective. To identify and comment upon the specimens of stem modifications.

 EXPERIMENT 7.2

Objective. To identify and comment upon the specimens of stem modifications.

REQUIREMENTS- Fresh or preserved specimens of modified stems, practical note book, pencil, eraser etc.

PROCEDURE

1.Observe the specimen carefully and note down its special features.

2.Draw the specimen on the practical note book. Depict only the parts actually visible in the specimen.

3.Write down the morphological features and the features of special interest of the specimen.

OBSERVATIONS AND COMMENTS

UNDERGROUND STEMS (UNDERGROUND STEM MODIFICATIONS)

1. GINGER/TURMERIC

Identification. Rhizome of Ginger (Zingiber officinale)/Turmeric (Curcuma domestica).

Comments

(i) It is an underground stem, which grows horizontally in the soil and sends up aerial leaves.

(ii) It has nodes and internodes and membranous scale leaves at the nodes.

(iii) It bears underground horizontal branches and is fleshy due to storage of food.

(iv) It bears adventitious roots on the lower side.

2. COLOCASIA (Kachalu)

Identification. Corm of Kachalu (Colocasia).

Comments

(i) It is a short, thick, usually unbranched, spherical or sub spherical underground stem which grows vertically in the soil.

(ii) It bears a number of circular nodes with scales which represent thin sheathing leaf bases.

(iii) It bears axillary buds at places.

3. ONION

Identification. Simple bulb of Onion (Allium cepa).

Comments

(i) It is an underground pyriform spherical structure that possesses a reduced disc shaped stem and several fleshy scales enclosing a terminal bud.

(ii) It bears a number of adventitious roots on the lower side of the stem.

(ii) It is covered by a sheath of dry membranous scales called tunic, hence, it is also called simple tunicated bulb.

4. GARLIC

Identification. Compound tunicated bulb of Garlic (Allium sativa)

Comments

(i) It is an underground stem with a reduced disc shaped stem bearing irregular concentric rings of bulblets or cloves around the central floral axis.

(ii) Each bulblet or clove consists of a sickle shaped fleshy bud.

(iii) Each ring of the bulblets in surrounded by a white membranous sheath or tunic.

(iv) A number of adventitious roots arise from its base.

5. POTATO

Identification. Tuber of Potato or Stem tuber of Potato (Solanum tuberosum)

Comments

(i) It is an oval or spherical underground swollen stem which does not bear adventitious roots.

Ii. It arises at the tip of special narrow underground branch called sucker.

(iii) It bears a number of spirally arranged depressions called eyes representing nodes.

(iv)Each eye bears a scale leaf in the form of a ridge. The eyes contain buds.

MODIFICATIONS OF SUB-AERIAL STEMS (CREEPERS)

1. LAWN GRASS/BRAHMI BOOTI/OXALIS

Identification. Runners of Lawn grass (Cynodon dactylon)/Brahmi Booti (Centella)/Oxalis

Comments

(i) They are thin horizontal or prostrate branches which develop at the bases of erect shoots called crowns. 

(ii) Each runner has one or more nodes that bear scale leaves and axillary buds.

(iii) Runner gives rise new crowns and tufts of adventitious roots at the nodes.

2. JASMINE/WILD STRAWBERRY

Identification. Stolons of Jasmine/Wild strawberry.

Comments

(i) They are elongated horizontal or arched runners which can cross over small obstacles.

(ii) Each stolon has one or more nodes possessing scale leaves and axillary buds.

3. CHRYSANTHEMUM/MINT

Identification. Sucker of Chrysanthemum/Mint.

Comments

(i) It is a special non-green slender stem branch which arises from the underground base of an erect shoot or crown.

(ii) It grows horizontally in the soil and ultimately comes out to form a new aerial shoot or crown.

(iii) Each sucker has one or more nodes with scale leaves and axillary buds.

4. PISTIA (Water Lettuce)/EICHHORNIA (Water Hyacinth)

Identification. Offsets of Pistia (Water Lettuce/Eichhornia (Water Hyacinth).

Comments

(i) They are one internode long runner like branches found growing on the mud or water level.

(ii) It is spongy and bears clusters of leaves and adventitious roots at the nodes.

MODIFICATIONS OF AERIAL STEMS

1. PASSIFLORA/CUCURBITA/GRAPE VINE (Vitis vinifera)

Identification. Stem tendrils of Passiflora/Cucurbita/Grape vine (Vitis vinifera).

Comments

(i) These are thread like sensitive structures which can coil around a support and help the plant in climbing.

(ii) They may be branched (in Cucurbita, Vitis)or unbranched (in Passiflora).

(iii) The branched stem tendrils may bear scale leaves in the region of forking.

(iv) They are axillary (in Passiflora), extra axillary (in Cucurbita) and leaf opposed (in Grapevine).

2. CITRUS/DURANTA/BOUGAINVILLEA

Identification. Stem thorns of Citrus/Duranta/Bougainvillia.

Comments

(i) They are stiff, sharp structures which have lost their growing point and become hard.

(ii) They arise in the axils of leaves.

(iii)In Duranta stem thorn may bear small foliage leaves. In Bougainvillia the thorns are curved.

Iv. Stem thorns reduce transpiration and also check browsing by animals.

3. OPUNTIA/MUEHLENBECKIA/EUPHORBIA TIRUCALLI

Identification. Phylloclade of Opuntia Muehlenbeckia.

Comments

(i) They are flattened or cylindrical (in E.tirucalli) green stem of unlimited growth which have taken over the function of photosynthesis.

(ii) True leaves are caducous.

(iii) In Opuntia, the flattened stem is thick, fleshy and segmented or jointed. Each segment develops in the axial of a caducous leaves and bear leaf spines in small areas called aerolae. The stem also store water, mucilage and latex.

(iv) Phylloclade help the plant to reduce transpiration.

4. RUSCUS/ASPARAGUS

Identification. Cladodes or Cladophylls of Ruscus/Asparagus.

Comments

(i) These are green stems of limited growth (usually one internode long) which have taken over the function of photosynthesis.

(ii) The true leaves are reduced to scales or spines, which bear cladodes in their axils.

(iii) In Ruscus the cladodes are leaf like in appearance which bear a floral bud in the middle of the cladode.

(iv) In Asparagus, the cladodes are slightly flattened and fleshy which develop in clusters in the axils of scale leaves.

(v) Cladodes are modification to reduce transpiration.