40 MORPHOLOGY OF STEMS AND BRANCHES. [LESSON 6. 



96. Subterranean Stems and Branches, These are very numerous 



and various ; but they are commonly overlooked, or else confounded 

 with roots. From their situation they are out of the sight of the 

 superficial observer : but if sought lor and examined, they will well 

 repay the student's attention. For the vegetation that is carried on 

 under ground is hardly less varied, and no less interesting and im, 

 portant, than that which meets our view above ground. All their 

 lorms may be referred to four principal kinds ; namely, the Rhizo- 

 ma or Rootstock, the Tuber, the Corm, and the Bulb. 



97. The RootstOCk, or Rhizoma, in its simplest form, is merely a 

 creeping stem or branch (80) growing beneath the surface of the 

 soil, or partly covered by it. Of this kind are the so-called creeping, 

 running, or scaly roots, such as those by which the Mint (Fig. 64), 

 the Scotch Rose, the Couch-grass or Quick-grass, and many other 

 plants, spread so rapidly and widely, " by the root," as it is said. 



That these are really stems, and not roots, is evident from the way 

 in which they grow; from their consisting of a succession of joints; 

 and from the leaves which they bear on each joint (or node, as 

 the botanist calls the place from which leaves arise), in the form of 

 small scales, just like the lowest ones on the upright stem next the 

 ground. Like other stems, they also produce buds in the axils of 

 these scales, showing the scales to be leaves ; whereas real roots 

 bear neither leaves nor axillary buds. Placed, as they are, in the 

 damp and dark soil, such stems naturally produce roots, just as the 

 creeping stem does where it lies on the surface of the ground ; but 

 the whole appearance of these roots, their downward growth, and 

 their mode of branching, are very different from that of the subter- 

 ranean stem they spring from. 



98. It is easy to see why plants with these running rootstocks take 

 such rapid and wide possession of the soil, often becoming great 

 pests to farmers, and why they are so hard to get rid of. They are 



FIG. 64. Rootstocks, or creeping subterranean branches, of the Peppermint. 



