POTATO 



463 



tured by the leaves passes down the stem, and from the middle 

 bud in each leaf-axil below ground a thin rhizome develops, 

 which, after reaching a variable length, generally forms a new 

 tuber at its end (Fig. 144). When the old dead tuber has been 

 exhausted of its store of food, it still contains water obtained 



Fig. 144. — Potato plant raised from an old tuber, and showing the arrangement and 

 nature of parts below ground. ^ a ground line ; b old tuber showing short, stiff stem 

 / produced during germination in the light before being planted ; o and n branches 

 from ty the tip of n has been broken off; o stem which has come above ground, cut off 

 at in; c rhizome, the end of which has developed into a tuber d^ upon the latter are 

 seen buds at e; f lateral bud on c ; p a rhizome similar to c, but which has not yet 

 formed a tuber ; r roots (adventitious). 



from the surrounding soil, and acts as a reservoir for the growing 

 plant in the dry part of the season. 



It must be observed that rhizomes only produce tubers when 

 they are kept in the dark, hence the value of ' earthing up,' 

 and the necessity of doing it at intervals so that newly-formed 

 rhizomes resembling / in the above Fig. may be properly ex- 



