12.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 57 



case that the first leaves of young plants are of a form different 

 from, and usually simpler than, that of those which are subse- 

 quently produced, and exhibit a greater resemblance to those of 

 allied plants. Thus, Eucalyptus globulus has at first oval dorsi- 

 ventral leaves, and subsequently elongated isobilateral leaves. 

 Again, the primary leaves 

 or cotyledons, when they 

 develope into foliage 

 leaves, are always dif- 

 ferent in form from the 

 subsequently developed 

 foliage-leaves, being much 

 simpler. In many water- 

 plants, the submerged 

 leaves are different from 

 those which float at the sur- 

 face ; thus, in many species 

 of Potamogeton, the sub- 

 merged leaves are narrow 

 and ribbon-like, whereas 

 the floating leaves are 

 broadly elliptical ; in many 

 aquatic species of Ranun- 

 culus, the former are finely 

 divided, whereas the latter 

 have a circular lamina. 

 Again, the submerged 

 leaves of Salvinia are fila- 

 mentous, whereas the float- 

 ing leaves are flattened 

 and oval. 



The simultaneous occur- 

 rence of two forms of 

 foliage-leaf on a plant is 

 termed heterophylly . 



In certain plants the 

 foliage-leaves assume re- 

 markable forms in connection with their adaptation for catching 

 small animals or for collecting water (e.g. Nepenthes, Cephalotus, 

 Sarracenia, Utricularia, Dischidia, etc.). In these the lamina is 

 metamorphosed into a pitcher or ascidium. The development of 



FIG. 36. Three forms of leaves on the stem of 

 Maianthemum bifolium (nat. size) : N catapbyllary 

 region; L region of the foliage-leaves; H hypso- 

 phyllary region; d the bracts; b the flowers in 

 their axils, w Roots. 



