10 «OTANY. 



expanded like a cake ; testiculate, when there are two large tuberoid roots 

 of nearly equal size. 



3. Ascendiuff Axis, or the Stem. 



The stem is the part of the plant usually exposed above the ground, and 

 bearing the leaves and flowers ; it is produced by the successive development 

 of leaf buds in a longitudinal and lateral direction. The stem bears diflferent 

 names, according to the character of the plant. Thus, in ordinary herbaceous 

 plants, it is called caulis ; in the case of trees, truncus ; in shrubs, caudex ; 

 in grasses, culm ; in palms and ferns, stipe. When a distinct stem is present, 

 the plant is called caulescent, when it is absent, acaulescent. True stems are 

 sometimes absent in certain plants, which consist merely of expansions of 

 cellular tissue, in the form of ajiJirenrations of cells. Such are called Thai- 

 logens, or Thallophj/tcs, and are represented by Chara, Conferva, and Alga. 



Stems, although more generally firm and erect, are sometimes weak, and 

 either lie prostrate {procumbent stems), or climb like the ivy by means of 

 suckers {scandent), or twist round other plants {volubile). The direction of 

 the twist may be either from right to left, as in Convolvulus, or from 

 left to right, as in the Honeysuckle. Some plants exhibit both directions 

 alterna'tely. The twining plants have generally herbaceous stems ; some, 

 however, are woody, as the Clematis, Vine, Honeysuckle, &c., whose 

 stems are called Sarfnenta. Woody climbers are very common in 

 tropical climates, where they are called Lianas. In some cases, the lateral 

 extension exceeds the longitudinal, as in Testudinaria and some Cacti. 



There are certain points along the stems, at which leaf buds and branches 

 appear ; these are called nodes, and generally occur symmetrically. The 

 spaces between the nodes are called internodes. A branch is but the 

 development of a leaf bud from one of the nodes. Spines are abortive 

 branches, and, in many cases, by change of culture, may be developed into 

 leaf or fruit bearing branches. 



When the stem is woody and continues to increase indefinitely, we have 

 either trees or shrubs ; trees when there is but one stem, shrubs when there 

 are several stems, mostly of equal size, springing up together from the ground. 

 A division of the shrub is sometimes made into the true shrub {frute.v), where 

 there is a short stem ; under shrub {suffrutex), where this is hardly evident ; 

 and low shrub {dumus), where the whole plant is low and spreading, the 

 branches springing up together as a multitude of stems at or near the 

 ground. The equivalent terms are arborescent, fruticose, suffruticose, and 

 dumose. 



The transverse section of the stem, though generally circular, may be 

 oval or even bounded by straight lines and angles. The various terms 

 applied are, terets ; half-terete ; compressed ; plano-com^pressed ; two-edged ; 

 acute-angled ; obtuse-angled ; triangular ; quadrangular ; quinquangu- 

 lar : octangular ; multangular ; triquetrous, &c., whose significance is suffi- 

 ciently evident, with the exception, perhaps, of the last, which refers to a stem 

 with three concave faces. 

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