CHAPTER II. THE STEM. 



15 



the scars of scales, sends off roots usually more abundantly from 

 the under surface, and commonly has its upper surface more or 

 less distinctly marked with the scars or withered remains of the 

 bases of aerial stems of previous years. The terminal bud is 

 usually conspicuous. A rhizome may either be slender and 

 extensively creeping, as in Couch-grass and Carex, Fig. 21, or 

 thickened and fleshy, as that of Solomon's Seal, Fig. 22. 



Fig. 21. — Creeping rhizome of a 

 species of Carex. 



Fig. 22. — Thickened rhizome of Solomon's 

 Seal. 



The Tuber is a short and excessively thickened underground 

 stem, borne usually at the end of a slender, creeping branch. 

 The tubers of the Artichoke and Potato, Fig. 23, are examples. 

 The creeping branches usually perish in autumn, setting the 

 tubers free from the parent plant. Since they grow in the spring 

 and produce new plants, they are efficient means of propagating 

 the species. They may readily be distinguished from tuberous 

 roots like those of the Sweet-potato, by the "eyes," which are 

 axillary buds. 



Fig. 23. — Tubers of the Potato in va- 

 rious stages of development. 



Fig. 24. — Longitudinal sec- 

 tion of the corm of the Crocus. 



The Corm is an excessively thickened, erect, underground 

 stem, covered with thin leaf-scales on the surface. The corms 



