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 : 



Fia. 28. — ^UuDEROROtrND Rhizome of Cottch-Gbass. 



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 



Fio. 29. — Undergkotjnd Khizoms 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 



