116 GENERAL BOTANY 



and becomes the leafy stem, and appear to pass 

 gradually into the ordinary leaves. We conclude,, 

 therefore, that these scales are leaves reduced to mere 

 scales, because, being underground, they cannot do the 

 ordinary work of leaves, and that therefore the axis 

 is part of the shoot, and not a root just as is the 

 under-ground branch of the potato plant, only here 

 the axis is much thicker and the internodes very 

 short. An under-ground stem of this kind is termed a 

 rhizome (which means root-like), or sometimes root- 

 Stock, and is of the same nature as the root-stock 

 of LAUNEA, except that it is horizontal instead of 

 vertical. 



In a few cases the part which comes up above 

 ground is not the end of the horizontal rhizome itself, 

 but a side branch developed from a bud in the axil of 

 one of the scale-leaves. But in most cases (e. g. in 

 CANNA and ACORUS CALAMUS) the end of the rhizome 

 itself turns up, and becomes the leafy shoot, and its 

 horizontal growth is continued by a lateral branch r 

 so that the whole horizontal under-ground part is a 

 sympodium (chapter viii, section 2). 



In some plants again, e.g. CROCUS and COLOCASSIA,. 

 there is a very thick and short root stock, of the shape 

 of a ball and covered with thin papery scales, which like 

 those of the Canna rhizome, are reduced leaves. This 

 is termed a corm. At the beginning of each growing sea- 

 son, a terminal bud shoots up from the apex of the 

 corm, and becomes a leafy shoot bearing leaves and 

 flowers, and dies down again at the end of the season. 

 New corms are formed at the side of the old by devel- 

 opment of the axis of axillary buds. 



