210 



HUTCHINSON'S POPULAR BOTANY 



these bundles provided with vitally active cambium ;' so that when 

 cease to grow (at an early stage in the history of the plant) the stem 

 also ceases to increase in thickness. The section of a stem of Ravenna 

 Grass (Eriantkus ravennce), which is shown in fig. 262,^ contains a portion 

 of one of these closed nbro-vascular bundles. Flower^ess Plants, or Crypto- 

 gams, usually do not contain them at all ; but where they are present they 

 sometimes form an irregular and broken ring near the outside of the stem, 

 as in the Ferns, and in other cases constitute the axis of the stem, and are 

 solitary. The Pillworts (Pilularia, fig. 267), a family of flowerless plants 



specially partial to 

 marshy and inundated 

 ground, offer interest- 

 ing examples of axial 

 fibro-vascular bun- 

 dles. All the Flower- 

 ing Plants, and those 

 among the Crypto- 

 gams which have 

 these bundles in their 

 stems, also contain 

 them in the roots ; so 

 that a system of ves- 

 sels extends from root 

 to leaves in each 

 plant, and forms, as 

 we were seeing in 

 Chapter III., the 

 skeleton or framework 

 on which the plant is 

 built up. 



The external forms 

 of stems exhibit even 

 greater variety than 

 the external forms of 

 roots. Some stems 



are very much like roots, not in their forms merely, but also in their habits. 

 We allude to those which grow underground to rhizomes, tubers, bulbs, 

 and corms. 



Rhizomes, of which the Flag (Iris}, Solomon's Seal (Polygoncttum,, figs. 265 

 and 269), and Lily of the Valley (Convallaria majalis) offer familiar examples, 

 are subterranean stems of horizontal growth, which give off roots below and 

 leaf- and flower-bearing shoots above. Such stems are always spoken of 

 as roots by the old writers. Gerarde, for example, refers to the rhizome of 

 the Iris as " gladen rotys " in the following curious recipe for a cosmetic : 



FIG. 263. PILLWORT (Pilularia globulifera). 



Transverse section of stem showing axial fibro-vascular strand. P is the paren- 

 chyma, surrounded by the dark ring of xylem, outside of which is the bast (-B) with- 

 in the bundle sheath. Outside this again are the cortex and epidermis. 



