30 



MORPHOLOGY 



of a plant with hard and woody tissues. Plants with 

 a single woody trunk of a large size, which usually 

 branches higher up, or sometimes remains unbranched, 

 are known as trees; whereas shrubs are low dwarf 

 trees, or woody plants, with several stems from the 

 same root. The terms culm and haulm are often 

 used in speaking of the stems of Grasses, and caudex 

 in speaking of the unbranched 

 stems of Palms. 



In some plants the stem be- 

 comes flattened out somewhat 

 like a leaf, and is green like 

 the latter. Such leaf-like stems 

 are known as cladodes. One 

 of the best examples commonly 

 met with in gardens is Cocoloba 

 platyclada (Plate I), in which 

 the stem is flat like a ribbon, 

 and of a shining green colour. 

 That it is not a leaf but a true 

 stem is evident from the fol- 

 lowing considerations, namely, 

 that it is divided like a stem 

 into distinct nodes and inter- 

 nodes; that it bears, when 

 young, small leaves on its mar- 

 gins, which, however, fall off as the stem develops; that 

 the surfaces look sideways, instead of up and down as 

 in leaves; and that both the surfaces are equally green, 

 in other words, one surface is not deeper green than the 

 other, as in leaves. Cladodes are homologous with 

 •stems but analogous with leaves. Another common 

 example of a Cladode is nag-phani or phani-monsha 

 iPpuntia Dillenii) (fig. 26). Several species of Cactus 

 and siju {Euphorbia) are more or less of this nature.. 



Fig. 26. — Prickly Pear or Phani- 

 monsha {Optintia Dillenii) 



