118 RHIZOME [CH. 



nodes in damp situations or in wet seasons, while offsets 

 frequently strike root before separating, or before their 

 connecting stolon dies away. 



Rhizomes are subterranean creeping stems, and their 

 own leaves, the presence of which at once distinguishes 

 them from roots, are small and not green, excepting in 

 cases where (e.g. Bracken Fern) they are first elevated 

 above ground into the light by the upgrowth of long leaf- 

 stalks. 



While the definition of the rhizome is easily applied 

 in most cases, it must not be forgotten that many perennial 

 super-terranean stems which creep close to the ground 

 may gradually sink in partly by the drag exerted on them 

 by their roots and partly by the rising of the surface of the 

 soil as time goes on e.g. some creeping Willows. More- 

 over some plants, such as the Potato and Mint, throw out 

 both underground and super-terranean creeping shoots, 

 apparently according to the level of insertion of the leaves 

 from the axils of which they spring ; while the thick 

 rhizomes of the common garden Iris (I. germanica) are 

 as often on the surface of the ground as below. These 

 remarks will suffice to show that no essential difference in 

 principle exists between the two classes of creeping stems 

 subterranean and super-terranean. 



The rhizome of the common Bracken Fern grows 

 horizontally some 6 8 inches below the surface of the 

 ground, and throws up one leaf each year from a point 

 about 2 inches or so behind the tips, which is growing 

 slowly forwards. If we take a rhizome at least four 

 or five years old, and dig it up when the current year's 

 leaf is fully expanded above ground in the summer, 

 there will be found a younger leaf, still underground 

 and not expanded, about half-way between the tip and 

 the expanded leaf: this leaf will come up into the air 



