STEMS ABOVE GROUND 



33 



it supports a mass of leaves very close to the root and is known 

 as a crown or acaulescent stem, or it may be more or less elong- 

 ated, as in the case of many herbaceous plants and trees. The 

 elongated stems may bq erect, as in the case of trees, but 

 extremely variable in size and form. Two well-defined types of 



FIG. 21. Twig showing alternate buds. 



the stems are the excurrent (Fig. 25), in which we find a tree 

 with a central axis or trunk giving off numerous small branches, 

 like the pine, and the deliquescent (Fig. 26), in which the main 

 trunk sub-divides by branching and loses its identity as in the 

 oak and elm. Stems belonging to either of these types vary 



FIG. 22. a, cross-section of dicotyledonous FIG. 23. a, cross-section of monocoty- 

 Btem; b, fibrovascular bundle from same, ledonous stem; b, cross-section of fibro- 



vascular bundle of same. 



greatly in the method of arrangement of the branches. Persons 

 who have given some attention to this subject can recognize 

 many trees by their style of branching. 



However, many elongated aerial stems cannot stand erect, 

 but are decumbent, or leaning, as in the case of many berry 

 plants ; or prostrate, as in the case of those plants which trail 

 3 



