292 



BOTANY. 



Surface. — Many stems are smooth, especially when young ; but as 

 they grow older they generally become more or less roughened. 

 They may be irregularly roughened, as in many tree-trunks, or they 

 may be somewhat regularly furrowed. Many stems are hairy, the 

 degrees being noted as downy (when soft and not abundant) ; silky 

 (when close and glossy) ; mllous (when long and spreading); hispid 

 (when short and stiff), etc. Other appendages of the surface are 

 prickles, warts, scales, etc. 



Color. — Note the color of the surface of all parts of the stem, in- 

 cluding the branches and twigs. 



Structure. — In some stems the softer tissues predominate; these 

 are herbaceous, and the plants are herhs. In others the harder tissues 

 predominate ; these are woody or ligneous plants, ' and are either 

 shrubs (which are not more than a couple of metres in height, and 

 generally have more than one stem) or trees (which have a single 



FiQ. 178. 



Fig. 179. 



Fig. 178.— Cross section of the stem of an oak-tree thirty-seven years 

 old, showing the annual rings, rm, the medullary rays ; m, the pith 

 (medulla) . 



Fio. 179.— Cross section of the stem of a palm-tree, showing the scattered 

 bundles. 



stem, and often attain the height of many metres). It must be re- 

 membered that intermediate forms of all degrees occur between 

 herbs and shrubs, herbs and trees, and shrubs and trees. 



Duration. — Some stems live for but one season, and are known as 

 annual ; others live for two seasons (gathering food the first, and 

 producing flowers and seeds the second), these are biennial ; those 

 which live for several or many years are perennial. 



Branching. — Most stems branch more or less, generally irreqular- 

 ly, rarely regularly ; the latter may be scattered, alternate, opposite, 

 or whorkd (i.e., three or more in a circle around the steic). 



