156 



EXTENSIONS AND APPENDAGES OF THE STEM 



branches. This gives us the forked or Bifurcating form of sym])0(linm, 

 often called (Hchotomous, though this term refers strictly to one in 

 which forking is caused by the vertical division of a terminal cell. 



Superficial Appendages to Stems. — Besides modified or unmodified 

 leaves or branches, stems may develop various other ai)i)endages. 

 When these are merely superficial, they are called Trichomes. The 

 characters of trichomes upon stems or leaves, particularly the latter, 

 are of the utmost importance in diagnosis. Their study, however, 

 save as to the surface characters which they collectively produce, 

 pertains to histology. The gross surface character so produced will 

 be taken up in connection with the leaf. 



Fig. 430. Aculeate stem of Chadaea. a, hooked prickles. 



Emergences or Outgrowths. — When ai)pendages are of deeper origin 

 they are called Outgrowths or Emergences. These may contain vascular 

 tissue, connected with that of the stem. Outgrowths are, for the most 

 l)art, in the form of spines, hooks (Fig. 436, a), warts, suckers (Ing. 459, 

 a, in this illustration a modified stem), or grasping organs. Usually 

 organs of this kind are the results of modifications of other organs, 

 rather than outgrowths. Both trichomes and outgrowths may be 

 regularly or irregularly disposed. 



