120 SYMPODIAL RHIZOMES [CH. 



centre. In this and other cases where the internodes are 

 very short and the bud comes nearly vertical from the soil 

 the rhizome is often termed a root-stock : other examples 

 are Trillium, Cicuta, Scabiosa, Polygonum Bistorta, and 

 some Water-lilies, &c. 



In sharp contrast to these monopodial rhizomes are 

 those which, like the Solomon's Seal, Iris, Bamboo, Sweet 

 Flag (Acorus, Fig. 51), Ginger, &c., where the apical bud 

 grows forward for a time, forming scale-leaves and roots, and 

 then turns upwards to develope its apex as the current year's 

 shoot. After the vegetative period this shoot dies down, 

 and a lateral bud from the axil of one of the subterranean 

 scale-leaves grows forward as the segment for the next 

 year, and will in its turn send its apical portion up into 

 the air next season, to die back in turn, and be succeeded 

 by another axillary bud, and so on. In these cases the 

 growth of the rhizome is definite or limited, and an old 

 specimen really consists of series of segments, each of 

 which was the branch for its vegetative season : it is a 

 sympodium. 



In the cases given, and in very many others such as 

 Asparagus, Polygonum cuspidatum, Lunaria rediviva, 

 Sparganium, Butomus, Convallaria: Tway-blade, Coral- 

 lorrhiza and other orchids, &c., the rhizomes are more or 

 less thickened and fleshy, and often have their outer walls 

 evidently protected by strengthening layers. These facts 

 are in accordance with their office as storage-reservoirs. 

 The leaves above ground make far more organic food- 

 materials during the period of their exposure to the light 

 and air, than is necessary for their present needs : the 

 surplus is deposited as starch or in other forms in the 

 underground rhizomes, and it is at the expense of these 

 stored materials that the new segment developes next 

 year and grows sufficiently to send up and expose a new 



