UNDERGROUND STKMH. 



105 



culms. They are jointed, and usually hollow except at 

 the joints. 



151. Besides the stems which grow above ground, 

 there are varieties to be found below the surface. Pull 

 up a Potato plant, and examine the underground portion 

 (Fig. 136). It is not improbable that you will regard the 

 whole as a mass of roots, but a very little trouble will 

 undeceive you. Many of the fibres are unquestionably 



Fig. 136. 



roots, but an inspection of those having potatoes at the 

 ends of them will show you that they are quite different 

 from those which have not. The former will be found to 

 be furnished with little scales, answering to leaves, each 

 with a minute bud in the axil ; and the potatoes them- 

 selves exhibit buds of the same kind. The potato, in 

 short, is only the swollen end of an underground stem. 

 Such swollen extremities are known as tubers, whilst the 



Fig. 136. Tubers of .hj Potato. 



