652 DEFINITION AND CLASSIFICATION OF STEMS. 



allied grasses, clothed with sheathing, membraneous scales; third, the erect and 

 fleshy stems of the Balanophorese and Orobanchacese, covered with dry scales (c/. 

 figs. 41 and 42); fourth, the branched stems of Lathrcea, lying embedded in the earth, 

 covered with large fleshy scales (cf. fig. 37); fifth, the coral-like scaly stems branch- 

 ing in all directions, which have no roots and are only covered with delicate scale- 

 leaves, as shown by Bj^ipogium (cf. p. Ill) and by the Coral-root {Corallorhiza 

 innata); sixth, the stems of the Tooth-cress (Dentaria), creeping underground with 

 thick, fleshy scale-leaves and clearly defined roots; seventh and last, the cylindrical, 

 subterranean stems with weak membraneous scale-leaves and many roots, as in 

 Solomon's Seal (Convallaria Polygonatum), the Sweet Spurge (Euphorbia dulcis), 

 and numerous other perennial undershrubs. Subterranean scale-leaf stems developed 

 as elongated shoots are classed together in botanical terminology under the name 

 "root-stock" or "rhizome" (rhizoma); the term "creeping stem" (soboles) is applied 

 to the thin, branching scaly stems which often creep for a considerable distance 

 under the ground. 



In the forms belonging to the first, third, fourth, and fifth groups, just enumer- 

 ated, the scaly stem passes directly into a floral stem, i.e. on the same stem below 

 are to be seen scale-leaves which stand in no direct connection with the processes 

 of fertilization, and above them perianth leaves, as in the Rafilesiaceae (cf. figs. 44 

 and 45), or bracts, as in the Broom-rape and Toothwort (cf fig. 37). In these plants 

 no green foliage leaves are developed; they are unnecessary, because these plants 

 are all parasites or saprophytes, and do not require to manufacture organic com- 

 pounds for themselves, but derive the material necessary for their further growth 

 from their host, or from the humus of the forest ground. In plants of the other 

 groups, of which Dentaria, Couch-grass, and Solomon's Seal may be taken as types, 

 two kinds of shoots are developed: — Shoots whose stem is beset only with scale- 

 leaves without chlorophyll, and those which branch off" from these grow up above 

 the ground, and there unfold green foliage-leaves. Here, too, must be mentioned 

 those strange plants whose perennial underground stems develop two kinds of 

 shoots which appear above ground; — first, shoots whose stem is covered below with 

 scale-leaves, but which bears flowers above and later on when these first shoots 

 begin to wither, leafly, flowerless shoots whose green leaf-blades unfold in the 

 sunlight. This remarkable division of labour is observed in many Alpine plants, 

 in species of Butter-bur (Petasites), and in the widely-distributed and well-known 

 Colt's-foot (Tussilago Farfara). 



Green scaly stems which develop as elongated shoots are obviously all aerial, 

 or rather, they grow above the ground and the cortex of their stems becomes 

 gi-een so far as the light can influence them. That part of the shoot which remains 

 hidden in the dark earth does not become green, and many such shoots, e.g. those 

 of Asparagus, are white and without chlorophyll in the lower half, their upper 

 portions alone being green, viz. the small needle-shaped branches (phyllocladia) 

 growing out from the axils of the small scale-leaves. Amongst the gx-een scale-leaf 

 stems must be included the cactiform plants, the switch plants, and the plants with 



