I04 



BOTANY AND PHARMACOGNOSY. 



characterized by an anomalous stem-structure, the tracheae being 

 very large. 



Stems vary furthermore in size and form. While most stems 

 are more or less cylindrical or terete, other forms also occur, as 

 the flattened stems in the Cactacese ; triangular in the Cyperaceae, 

 and quadrangular in the Labiatae and Scrophulariaceae. 



Fir.. 69. Polygonal um muUiflorum , a plant growing in tlie Northern Hemispheres and 

 Japan and producing a rhizome resembling our Solomon's Seal {Polygonatum biflorum). 

 A, rhizome placed artificially higher in the soil than the normal depth; its continuation 

 shoot has grown downwards. B, rhizome placed deeper than the normal depth; its con- 

 tinuation shoot has grown upwards. The dotted lines at h indicate the amount of annual 

 growth in the rhizomes A and B. C, a seedling rhizome. At the right is the seed, which 

 encloses the haustorial end of the cotyledon; H, primary root; n, lateral roots arising within 

 the axis of the shoot; a, posterior side of cotylar sheath; v, anterior side of the same; b, c, 

 katophyls (or leaves on hypogeous shoots) on the axis of the seedling. A and B, after 

 Rimbach; C, after Irmisch. (From Goebel's "Organography of Plants.") 



Hypogeous Shoots. While most stems attain a more or 

 less erect position as in trees and shrubs there are others which 

 bend over to one side, or lie prostrate on the ground, and in some 

 cases produce roots from the nodes, as in Mentha spicata. These 

 latter are known as stolons or runners. 



