42 



STEMS. 



[SECTION 6. 



prickles, such as those of Blackberry aud Roses, are only excrescences 

 of the bark, and nut branches. 



102. Equally s\ I'inns of 

 stems are charaetrrislie of the 

 Cactus family (Fig. 111). These 

 may be better understood by com- 

 parison with 



103. Subterranean Stems 

 and Branches. Tin 1 so are very 

 numerous and various; but they 

 arc commonly overlooked, or else 

 are confounded with roots. From 

 their situation they are out of or- 

 dinary sight; but they will well 

 repay examination. For the veg- 

 etation that is carried on under 

 ground is hardly less varied or 

 important than that above ground. 

 All their forms may be referred to 

 four principal kinds : namely, the 

 Rhizomii (R//i:oif) or R<i<>txt<><-h\ 

 the Tuber, the Corm or solid bulb, 

 and l.lie true Bulb. 



]<)*. The Rootstock, or Rhi- 

 zoma, in its simpler form, is 

 merely a creeping stem or branch 

 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. 97), the Couch-grass, or Quirk -grass, and manr 

 other plants, spread so rapidly and widely, " by (lie root,'' as it is said. 

 That these arc really stems, and not roots, is evident fnun the way in which 



Fio. 95. A brandling thorn of Honey Locust, Wins a " indurated leafless branch 

 developed from an accessory bud far above the axil : at the cut portion below, three 

 other buds (a) are concealed under the petiole. 



Fio. 96. Spine of Cockspur Thorn, developed from an axillary bud, as the leaf- 

 scar below witnesses: an accessory leaf-bud is seen at its base. 



Fia. 97. Rootstocks, or creeping subterranean branches, of the Peppermint. 



