REN R 121 Lec. 10

Specialized Stems

stem 

all of these have nodes, internodes, and axillary buds 

rhizomes

are horizontal stems that grow below ground, often near the surface of the soil and superficially resemble roots; they have scalelike leaves and axillary buds at each node with short to long internodes in between; adventitious roots are produced along the lower surface; functions as a food-storage organ (may be thick or slender) and can propagate; eg. ginger or bamboo

runners

horizontal stems that grow above ground along the surface with long internodes; in saxifrages and some other house plants, runners may produce new plants (propagative) at intervals as they grow out and hang over the edge of the pot; usually produced after the first flowers of the season (there may be several) with adventitious buds at alternate nodes to develop new plants; eg. strawberry

stolons

stems that are produced beneath the surface of the ground and grow in different directions (but not horizontal); some botanists find no difference between these and runners (variations of each other); eg. irish potatos have tubers produced at the ends of these

tendrils

A branch that is capable of clinging or coiling around structures to provide additional support; may be a modified stem or leave depending on anatomy eg. pumpkin

tubers

short and thickened stem that grow underground; composed of starch-storing parenchyma tissue; constitute the resting stage of various plants and enable overwintering; eg. potatos 

potatos

in irish or white —— plants, several internodes the the tips of stolons becomes tubers (a mature tuber becomes isolated after the stolon to which it was attached dies); the ‘eyes’ are nodes around the thickened stem consisting of axillary buds in the axil of a scalelike leaf (visible only in very young tubers); the small ridges seen on mature tubers are leaf scars

bulbs

large buds surrounded by numerous fleshy leaves, with a small stem at the lower end; Adventitious roots grow from the bottom of the stem, but the fleshy leaves comprise the bulk of the bulb tissue, which stores food; eg. onion (the fleshy leaves usually are surrounded by the scalelike leaf bases of long, green, above-ground leaves

corm

resemble bulbs but differ from them by being composed almost entirely of stem issue minus a few papery, scalelike leaves sparsely covering the outside; adventitious roots are produced at the base; function in food storage; eg. crocus, gladiolus

cladophylls

these stems are flattened and appear leaf-like (also known as cladodes or phylloclades); has anode bearing very small, scale-like leaves with axillary buds in the center (such as in butcher’s broom plant); eg. asparagus (the feathers are these), greenbriers, certain orchids, prickly pear cacti, etc.

english ivy

these stems climb with the aid of adventitious roots

boston ivy 

these tendrils have adhesive disks 

cacti

stout and fleshy stem adapted for storage of water and food

honey locust 

stems modified in the form of thorns