Answer:
Modifications of stem Stems are modified to perform various functions. Stem modifications are as follows:
(a) Stem tendril They may be branched with scale leaves in the region of branching (i) Axillary, e.g., Passiflora, (ii) Extra axillary, e.g., Luffa, Cucurbita, (iii) Scorpioid stem tendrids, e.g., Vitis vinifera, (iv) Floral bud, e.g., Antigonon.
(b) Stem thorns These are stiff sharp structures which are formed for reducing transpiration and protection from animals. Thorns are generally axillary, e.g., Citrus, Pomegranate, etc. In Alhagi the thorn bear flowers.
(c) Phylloclades They are green, photosynthetic, often succulent stems of indefinite growth. Function of leaves is performed by stem. Phylloclades are formed in an adaptation to dry habitats, e.g., Euphorbia soyleana, Opuntia.
(d) Cladodes (cladophylls) They are green photosynthetic stems of limited growth with leaves reduced to scales or modified into spines, e.g., Ruscus, Asparagus. Cladodes of Ruscus are leaf like, borne in the axils of scale leaves, having a floral bud and scale leaf in the middle.
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