26 COMPOUND ORGANS OF PLANTS. 



Fig. 5. 



Rhizoma of Solomon's Seal, (Polygonatum pubescens.) 



The Thizoma or underground stem grows after the manner 

 of ordinary aerial stems by the development of both lateral and 

 terminal buds. In Polygonatum pubescens the development of 

 the subterranean buds is alone terminal, but in other perennial 

 herbaceous plants the lateral as well as terminal buds of the 

 rhizoma are developed, and the subterranean branches, which 

 are called suckers, send up from the soil aerial stems. These 

 suckers when severed from the parent stem and planted will 

 grow into new plants. This mode of multiplying plants is 

 often resorted to by gardeners, and is called by them, propa- 

 gating by offshoots. 



The bulb. This form of underground stem is much varied. 

 It may be a scaly bulb, as in the lily, or a tunicated bulb, as 

 in the onion. These varieties of bulbs are justly regarded by 

 botanists as subterranean buds or undeveloped stems, being in 

 every respect similar to the ordinary leaf bud, except that as 

 they grow beneath the ground, the scales or imperfect leaves 

 which envelope them are more thick and fleshy. These retain 



