MODIFICATIONS OF FORM 



165 



length of which is swollen for storage in each successive year. That 

 of the previous year is depleted in each spring by the terminal flower, 

 and an axillary bud is distended as the season advances, so as to pro- 

 vide for the next season's growth (Fig. 124). The membranous bases 

 of its withered leaves cover the corm externally, while their axillary 

 buds may provide additional corms. Thus it is an upright branched 

 storage axis, with abbreviated growth. Similar distended axes 



Fig. 123. 

 Tuberous roots of the Dahlia. (After Figuier.) 



Fig. 124. 



Corm, or storage stem of Crocus. 



(After Figuier.) 



are found in many other perennials, e.g. the Tuberous Buttercup 

 {Ranunculus bulbosus), and the Pig-Nut (Conopodium denudatwn). In 

 other cases the storage is in lateral branches borne in large numbers, 

 as in the Potato and Jerusalem Artichoke. These will be considered 

 later. in relation to vegetative propagation, to which such developments 

 readily lead. The bulb, as in the Hyacinth, Snowdrop, or Lily, is 

 similarly an upright, abbreviated, perennial shoot, with its growth 

 interrupted by dormant periods. Its biology corresponds to that of 

 the corm ; but here the chief storage region is not the axis, which 

 remains small and broadly conical, but the bases of the leaves. The 



