Modified stems.
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<BR><LI> Rhizomes  (iris)  are  horizontal  stems  that grow just below the
surface, and can produce shoots from axillary buds along the stem.
<BR><LI> Bulbs  (onion) are underground shoots that store food in layers of
modified leaves.
<BR><LI> Stolons  (strawberry)  are  horizontal stems ("runners") that grow
along the surface. New shoots can form at axillary buds along each
runner.
<BR><LI> Tubers  (potatoes)  are  enlarged rhizomes specialized for storing
food.  The  "eyes" on a potato are axillary buds that can form new
shoots.