16 



OEGANOGEAPHY AND GLOSSOLOGY. 



up the lower portion of the stem; if the covering is slight, the tuber swells but 

 little ; if the light can penetrate to the stem, the tuber becomes green, and produces 

 rosettes of leaves. 



Props [fulcra) are a kind of aerial roots which spring from the axils of leaves, 

 or from various points of the stem in certain climbing plants [Ivy, fig. 47), which 

 are attached by them to walls or trees ; these organs are non-absorbent, but under 

 suitable conditions they behave like ordinary roots, as is seen with ivy cultivated for 

 edgings. 



Suckers (haustoria) are small warts upon certain parasitic stems [Guscuta, 

 fig. 48), whence issue true supplementary roots, which attach themselves to the 

 neighbouring plants, and draw nourishment from their juices. 



The stem is cylindiic or terete (c. cylindricus, teres), when a transverse cut 

 presents a circular outline [Cabbage) ;— compressed [c. compressus), when an elliptic 



stem with props. 



40. Pink. Nodose stem. 



48. Cuscuta. Stem with snclcei's (mag.), 



one, as if squeezed from opposite sides [St. John's Wort, Tutsan) ; — triangular or 

 trigonous [c. triangularis, trigonus), when a cut shows three sides [Carex) ; — square 

 [c. quadrangularis, tetragonus), when it shows four right angles [Lamium) ; — 

 pentagonal (c. quinquangularis, pentagonus), when it shows five faces and five angles 

 [Bramble) . 



The stem is glabrous [c. glaber), when there are no hairs on it {Horse-tail) ; — 

 smooth [Icevis), when, being glabrous, it presents no roughness, and its surface is quite 

 even [Tulip) ;— scabrous (c. scaber, asper), when its surface presents little inequalities 

 [Carrot) ; — striate (c. striatus), when it is marked with small raised longitudinal lines 

 or strice [Sorrel) ; — winged [c. alatus), when furnished with foliaceous expansions 



[Comfrey, fig. 66) ; — nodose [c. nodosus), when its nodes are tumid [Pink, fig. 49) ; 



pilose (c. pilosus), when it is furnished with long scattered hairs [Herb-Robert) • 



