THE GROWTH OP BOOTS AND STEMS. 183 



perennial, and forms flowers and new tufts of leaves year 

 after year, as in the Plantain, Daisy, and Dandelion. 



Most stems grow in the air, but many are buried in the 

 soil. Some are soft (herbaceous), others hard and woody 

 (chiefly in arboreous or arborescent plants, i.e. shrubs and 

 trees) . In our later studies we shall find that the stems of 

 plants assume an immense variety of forms in connection 

 with special adaptations. 



Many plants produce special branches which serve for 

 vegetative propagation, i.e. multiplication apart from seed- 

 formation. This is especially common among low-growing 

 or " ground-hugging " plants. 



218. Runners are long slender branches which grow along the 

 surface of the soil. They are easily studied in Strawberry, Daisy, 

 and Sweet Violet. In the House-leek and various Crassulas the 

 runners or " offsets " are short, and carry out large rooting buds from 

 the parent plant. 



The " suckers " of Rose, Raspberry, and Mint are lateral branches 

 arising below the level of the soil, which grow upwards to form sub- 

 aerial stems bearing leaves and flowers. The underground portions of 

 such stems resemble roots, and are white or pinkish in colour. Their 

 true character can, however, be told by their axillary exogenous 

 development, and by the occurrence of scale-leaves upon them. In 

 some cases (Roses and Poplars) the suckers arise from roots. 



219. Underground Shoots are commonly used for the 

 storage of food, and they may serve either for the main- 

 tenance of the life of the individual when the parts above 

 ground are killed by winter frosts, or for the production of 

 new individuals by vegetative propagation. They may be 

 distinguished from roots by the fact that they bear leaves or 

 buds, and by their origin from buds borne in the axils of 

 leaves or leaf-scales. The four chief types of underground 

 shoots are Rhizomes, Tubers, Corms, and Bulbs. 



220. The rhizome is a stout or slender stem, which usually 

 grows horizontally a short distance beneath the surface of the 

 soil. Stout and partially upright rhizomic stems are some- 

 times termed "root-stocks," but they can be distinguished 

 from roots by the fact that they bear leaves and buds, as 

 well as by their internal structure. Usually only small 

 brown membranous scale-leaves arise directly frcm the 



