MORPHOLOGY OF HIGHER PLANTS. 329 



bulblets, an important means of distributing the plants. The 

 thickened fleshy stems of Cactaceae are also regarded as storage- 

 organs. 



A CORM is intermediate between a true tuber and a bulb ; 

 it is more in the nature of a thickened internode, being surrounded 

 in some cases by thin, membranous scales, as in Crocus and 

 Colchicum. 



The function of the vegetative shoot is to absorb nutrition 

 from the earth as well as from the air. The shoot may be AERIAL 

 or SUBTERRANEAN. Some plants possess only aerial shoots or 

 UGHT-SHOOTS, as, for instance, trees, shrubs, and herbs that flower 



FIG. 187. Rhizome of African ginger showing scars of overground branch (Ls) and 

 hue's (k). The more or less parallel lines represent leaf-scars and scars of bud-scales, and 

 the small circles, root-scars. After Meyer. 



but once. Other plants possess both aerial and subterranean 

 shoots, and of these the subterranean shoot may exhibit some of 

 the peculiarities of roots, in that they do not develop chlorophyll 

 and produce secondary roots for the purpose of obtaining nutri- 

 tive substances from the soil. The SUBTERRANEAN SHOOTS are 

 generally destitute of true leaves and are furnished only with 

 membranous or sometimes thick, fleshy leaves which are bladeless, 

 pale, scale-like, or tubular. 



Depending upon the duration of the shoot (or, better, the 

 stem), plants are divided into HERBS, SHRUBS, and TREES. In 

 herbs the aerial shoots are herbaceous, while in shrubs and trees 

 they become woody and persist throughout many years. 



