CHAPTER IV. 



DIVIDED AND COMPOUND LEAVES. 



Development of the leaf The branching of the leaf Teeth and 

 lobes Venation Pinnate and palmate types Incision of the 

 leaf Compound leaves Segmentation Rachis, petiolule, 

 pulvinus, &c. Leaflets Description of compound leaves 

 Types of pinnate, palmate and tri-foliolate compound leaves 

 Types of simple lobed leaves. 



THE development of the young leaf in the bud shows us 

 that it always arises as a small hump of tissue on the side 

 of the more or less pyramidal end of the shoot-axis. See 

 Vol. I. Chap. iv. As this hump grows larger it expands 

 more and more according to the type of lamina to be 

 formed. If this is small and entire, the process of shaping 

 is comparatively simple ; but in many cases the expanding 

 leaf-incept soon begins to grow more rapidly in certain 

 directions from various points on its margins. This 

 branching of the leaf for that is what the process really 

 amounts to may be very slight, and result in nothing 

 further than the small marginal irregularities we have 

 termed teeth, and the leaf ends by being simple and 

 dentate, serrate, crenate, &c., as shown in Fig. 9. 



If the branching of the lamina goes further, and puts 

 out prominences too large, and involving too great a 

 proportion of the margin to be termed teeth, we call 

 them lobes, and the leaf is a simple lobed leaf (Fig. 11). 



