MODIFICATION OF FORM OR FUNCTION 165 



Acaulescent Plants. — The term Acaulescent, while strictly meaning 

 stemless, can, of course have no such application, as all flowering plants 

 possess a stem, even before germination occurs. The term is applied 

 to those plants whose stems are so short as not to become con- 

 spicuous. 



The Crown. — The stem of such a plant is called a Crown. The term 

 crown is also applied to the branching or leafy portion of any stem. 



Trees, Shrubs, and Undershrubs. — A plant possessing a woody and 

 erect stem rising singly to the height of fifteen (according to some 

 authorities, twelve) feet or more is denominated a Tree, or Arborescent 

 plant, although the precise application of such a term is impossible. 

 A perennial woody stem which has not these characters is called a 

 Shrub or a Fruticose stem. Very small shrubs appearing on causal 

 inspection as herbs are called Undershrubs or Suffruticose plants. 



Direction of Growth and Nature of Support. — As to the direction of their 

 growth and the nature of their support, stems may be Erect, in which 

 case they are erect through their entire length; Ascending, in which case 

 the base for a greater or less distance rests upon the ground, the terminal 

 portion becoming erect; Horizontal, in which case they are considered 

 as having no other support than the parent stem, from which they 

 extend at a right angle; Drooping, in which case they are first hori- 

 zontal, the outer portion becoming pendant; Pendant, or "Weeping," 

 when they are pendulous from their point of origin or almost therefrom; 

 Decumbent, when at first erect or supported by the parent, the outer 

 portion declined so far as to rest upon the ground; Rechning, when 

 resting upon some means of support elevated above the earth, as over 

 the tops or branches of other plants; Procumbent, when resting at full 

 length upon the ground without rooting at the joints; Repent, or 

 "Creeping," when prostrate and rooting at the joints (Fig. 445); 

 Twining, when supporting themselves by the twining of the stem itself 

 around a support; Climbing, when elevating and supporting them- 

 selves by other methods than a twining habit, the principal forms being 

 the Cirrhiferous, when cHmbing by tendrils (Fig. 431), and Aculeate, 

 when climbing by hooks (Fig. 436). 



Modification of Form or Function. — Modified Stems. — As to modifi- 

 cation of form or function, stems are subject to a somewhat elaborate 

 classification. 



They may be modified for the purpose of defence, that is into thorns 

 or spines (Fig. 453), although not all thorns or spines are transformed 

 branches. Some branches of this form remain so permanently, while 



