110 BRITISH PLANTS 
remain alive beneath the soil in the form of various 
xerophytic structures from which new shoots arise in the 
spring (see Geophytes, p. 62). 
Underground Perennating Organs found in herbaceous © 
perennials : 
Fic. 28.—UnprrGrounD Ru#IzoME or CovcH-GRASS. 
1. Rhizomes.—These are perennial underground stems 
bearing scales, buds, and roots (Figs. 28, 29). Rhizomes 
are not roots, though they are underground and carry 
roots. The leaves on subterranean stems are scaly when 
they do not come above ground, because, being in the 
dark, chlorophyll does not develop. The buds occur in 
the axils of these scales, or terminally at the extremity of 
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Fic. 29.—UnbDERGROUND RuIzoME oF Mint. 
the branches. Rhizomes are more or less thick and 
fleshy, containing a store of food-material which migrates 
to the brood-buds when they develop the aerial stems. 
When the rhizome is short, thick, and erect, as in some 
ferns, it is known as a root-stock. 
2. Tuberous Structures.—These are fleshy, hibernating 
organs stored with food. The fleshy part may be either 
