1. Modification of the stem Some of the most important types of modifications of stem are as follows: Underground modifications of Stem Sub aerial modifications of Stem Aerial modifications of Stem.

3. Underground modifications of the stem Many plants produce underground stems for perennation and food storage. They produce aerial shoots annually. Such stems resemble roots superficially but can be distinguishable from roots by presence of following features: Presence of nodes and internodes Presence of leaf scales, buds and adventitious roots at the nodes. Internal structure that resembles that of aerial stem and not of roo t.

4. Rhizome

5. It is fleshy, non-green underground stem with distinct nodes and internodes. Nodes bear dry leaf scales with axillary buds. Terminal buds are present. Adventitious roots arise from the lower side. A rhizome that grow obliquely is a root stock rhizome (e.g. Banana etc.) and when it grows horizontally it is a straggling rhizome (e.g. Ginger).

6. MODIFIED STEM Rhizome Horizontal stem, usually thick, that grows partially or entirely underground (iris, canna, sansevieria)

7. MODIFIED STEM Bulb A specialized storage organ (usually underground) composed of a compressed stem enclosed by fleshy or papery leaves or leaf bases. Middle A concentric or tunicate stem bulb enclosed by concentric or sheathing leaves or leaf bases (onion, garlic, amaryllis, tulip) Lower. A scale or non-tunicate bulb - stem enclosed by separate, thick (usually fleshy) scale-like leaf bases (lily)

8. Underground stem: bulb

9. Bulb A highly condensed, discoid stem with its upper surface a terminal bud and with many, fleshy leaf scale. Characterised by: * A cluster of adventitious roots that arise from the base Tunicated or scaly (covered by a sheath of dry membranous scale leaves, e.g. onion and garlic In case of garlic, the bulb consists of an aggregate of bulblets or cloves, each covered by its individual tunic. A scaly bulb is without a tunic, e.g., Lily.

10. MODIFIED STEM Corm Short, thickened, underground stem with few nodes and short internodes, usually enclosed by dry, scale-like leaves (gladiolus, crocus, taro)

11. Corm A condensed form of rhizome growing in vertical direction. More or less spherical with a flattered base Has distinct circular nodes and internodes Nodes bear leaf scales and axillary buds Adventitious roots arise either from its base or all over the body (e.g. Colocasia, Corcus)

12. MODIFIED STEM Tuber Large, underground storage organ formed by thickening or swelling of the sub apical portion of an underground stem (caladium, Irish potato, Jerusalem artichoke)

13. Stem tuber A swollen tip of an underground lateral stem (stolon) Covered by a corry skin with a number of small depressions called “eyes” Each eye represents a node, bearing one or more buds subtended by a leaf scar (= scale leaf) A big scar at one end (heel end) of a potato marks its attachment to the stolon Adventitious roots are usually absent (e.g. potato).

15. Sub aerial modifications of stem In sub aerial modifications, the stem is partly aerial and partly underground. Short aerial branches and adventitious roots develop at the nodes. Detachment of entire branch or a node can develop into a new plant. The plants are commonly known as creepers and their sub aerial stem modifications are meant for vegetative propagation.

16. Runner A runner is a creeping stem with long internodes, that run horizontally on soil surface. Nodes bear axillary buds, scale leaves and adventitious roots. Runner arises from an axillary bud. Runners break off and grow into individual plants, and thus help in vegetative propagation (e.g. Cynodon, Oxalis)

17. Runner

18. 2. Sucker: It arises from the basal, underground part of the main stem. It grows horizontally for a distance under the soil and then emerges obliquely upwards. It develops a leafy shoot and adventitious roots before separating from the mother plant. The common sucker- bearing plants are Chrysanthemum (Or. Sebati), Musa (banana), Mentha (Or podina), strawberry, pineapple etc.

19. Stolon A weak lateral branch that arises from the base of main stem After growing aerially for some time, it bends downwards to touch the ground, where its terminal bud gives rise to a new shoot and adventitious roots (e.g. Jasmine).

20. Stolon

21. Offset A short runner with one internodes long Originates from leaf axil, grows as a short horizontal branch Produces a rosette of leaves above and adventitious roots below (generally found in aquatic plants like Pistia (water lettuce), Eichhornia (water hyacinth)

22. Aerial modifications of stem Aerial stem or buds may get modified to perform such special functions as climbing, protection, food storage, vegetative propagation, etc.

23. Stem tendrils Stem or its branches get modified into green, thread like leafless structures called tendrils which are meant for climbing. Tendrils may be branched or un-branched. A scale leaf is always present at the point of branching of the tendril.

25. Stem tendril Stem tendrils are of four types: Axillary tendrils, e.g. Passiflora Extra-axillary tendrils, e.g. Cucurbita Leaf-opposed or apical bud tendrils, e.g. grapevine (Vitis) Floral bud or inflorescence tendrils, e.g. balloon vine

26. Thorns Straight, pointed, hard or woody structures which sometimes bear leaves, flowers or even may be branched (found in Citrus, Carrissa, and are for defense or climbing as in Bougainvillea).

27. Thorns

28. Phylloclades These are fleshy, green flattened or cylindrical branches of unlimited growth. The leaves are modified into spines or scales to check transpiration (Opuntia, Euphorbia, Casuarina)

30. Cladodes and Cladophylls

31. Cladodes or Cladophylls These are green cylindrical or flattened leaf- like branch of limited growth (e.g. Asparagus, the cladodes are one internode long and in Ruscus the cladodes are two internode long). They assist in photosynthesis.

32. MODIFIED STEM Thorn A stem modified into a short (usually), sharp point (e.g. Rosea)

33. MODIFIED STEM Spur A compressed stem with short internodes, usually bearing leaves, flowers and/or fruit. Many fruit trees bear flowers and fruits on spur shoots (e.g. apple, pear )

34. MODIFIED STEM Cladophyll A flattened stem, specialized for photosynthesis (e.g. Cactus)

35. MODIFIED STEM Pseudobulb Thickened bulb-like leaf (or stem) base that resembles a bulb (orchid)

36. MODIFIED STEM Stolon Horizontal stem, usually thin, that grows above ground, and usually forms roots and plantlets at nodes that contact the ground (grasses)

37. MODIFIED STEM Runner Slender stem with elongated internodes (Strawberry, Spider plant) The illustration is that of a spider plant (Chlorophytum comosum)

38. This stem does photosynthesis, stores water, but also produces a defense chemical: mescaline…a hallucinogen. Lophophora wiliamsii- peyote