GENEEAL MORPHOLOGY OF THE PLANT 61 



Indeed, the epipodium of the leaf is a branch syBtem rather than 

 a simple outgrowth. 



The main axis, though often winged, may be continued as a 

 supporting organ on which the branches known 3.S 2nnnce can 

 be recognised. The branches of the first order also frequently 

 remain cylindrical, and their secondary branches are the only 

 flattened portions. Sometimes, as in the leaf of the Fennel, all 

 the branches are cylindrical, and there is no flattened expansion, 

 the leaf appearing almost filamentous. Similar filamentous 

 leaves are found in some of the Water Crowfoots. 



The branching of the epipodium proceeds on the same lines 

 as that of the stem ; it is dichotomous in some of the Hymeno- 

 phyllaceae, a family of Ferns ; it is monopodial in many Dicotyle- 

 dons, where the branches are produced either acropetally or 

 basipetally, according to the position of the region of active 

 growth ; it is cymose in many other Dicotyledons. It is usual 

 to describe the types of leaves derived from the racemose and 

 cymose modes of branching as pinnate or palmate respectively, 

 both showing considerable variety of form. 



When the axis of the epipodium remains cylindrical, and 

 its branches of the first order become separately winged, the 

 appearance is presented of a number of small winged expan- 

 sions, each attached to the axis and each apparently indepen- 

 dent. Such a leaf is called compound. According to the nature 

 of the brandling we get the pinnate or the palm,ate leaf, the 

 separate branches being called leaflets. When the apex of the 

 epipodium of the pinnate leaf is winged lilje the branches, the 

 leaf is said to be imparipinnate {fig. 93) ; when there is no ter- 

 minal winged expansion, it is paripinnate (fig. 94). Various 

 forms of leaves of both tjTpes will be described later. 



When the axis is winged as well as its branches, the wings 

 of both are usually more or less united, giving rise to the 

 appearance of a single much-divided lamina. Such leaves, 

 however much divided, are classed as simple leaves. In many 

 cases with much-branched epipodia the main axis and the 

 secondary axes are not winged, while the tertiary axes and 

 the ultimate branches are both winged, and show a fusion of 

 the wmgs, as in fig. 97. Such a leaf shows a combination of 

 the simple and compound forms ; it is common among the 

 Umbelliferee. 



The fusion of the wings of the axis and its branches shows 

 almost every stage of completeness from the compound leaf to the 

 simplest flattened expansion. Indeed, in many of the latter the 



