MODIFICATIOX OF FORM OR FUXCTIOX 167 



case of Ampelopsis (Fig. 459, a). In this case the tip of the branch or 

 stem becomes flattened and attaches itself very tightly to the supporting 

 surface; so tightly, in fact, that a portion of stone or a splinter of wood 

 may be torn from its support before the disk can be made to separate 

 from it. Plants which grow in the water or in places subject to inunda- 

 tion may have portions of their stems inflated into bladdery forms to 

 insure a floating condition. Such structures are, however, more com- 

 monly of a leafy nature. 



Cladoidia or Cladophylla. — Stems may become modified for the per- 

 formance of the ofiice of leaves. Such a stem is called a Cladoidiiim or 

 Cladophyllum (Figs. 457 and 460). For this purpose the whole stem 

 may become modified into a single leaf-like organ, as in the case of 

 certain aquatics, in which case it is known as a Frondose Stem (Fig. 

 456). Upon the other hand, separate portions of the stem or separate 

 branches thereof may become thus modified, as in the case of the so- 

 called "leaves'" of the species of Asparagus cultivated as a decorative 

 plant under the name of Smilax (Fig. 457: a, leaf; b, branch). Some- 

 times a stem or a joint of one, at the same time that it becomes modified 

 to perform the office of a leaf, performs the ordinary offices of a stem, 

 or important storage functions as well, as in the case of the Opuntia 

 (Fig. 45S), and the Phyllanihus (Fig. 460). Such stems are called 

 ConsoHdated. Branches hke those in Fig. 460, modified to perform 

 the leaf-function, are called Phylhdadia. 



^lany trees have been encountered by the author in tropical America, 

 the stems and branches of which are hollow (denominated fistulous), 

 affording permanent homes to m^Tiads of ants, which, deriving their 

 support from the tree, are supposed to confer some compensatory 

 benefit upon it. They at least protect the tree against animal attacks, 

 being m all cases extremely savage and venomous. 



Besides such specially modified forms, a number of ordinary forms 

 are characterized by the adjectives Terete, Cyhndrical, Compressed, 

 Triangular, Quadrangular, Alate or Winged, Costate or Eibbed, Chan- 

 nelled, Striate, and so on. In this connection the terms applicable to 

 the superficial characters of barks already described, and those con- 

 nected with leaf-attachment, to be described farther on, should be 

 studied. In addition to the above-mentioned stem-forms, which admit 

 of ready classification, we have a large number of modifications to efl^ect 

 special purposes, which must be considered indi\idually. As these 

 possess but a slight interest in relation to pharmacognosy, we refer the 

 interested student to more general works on botany. 



