LEAVES AND BUDS. 



135 



PALMATE 



Next observe the different kinds of margins of the blades. Some 

 are even or entire, while others have sharp teeth which usually point 

 towards the tip of the blade and resemble the teeth of a saw (serrate 

 leaves), or have rounded teeth 

 (crenate leaves). Note also the 

 hairy (ciliate) margin of the Beech 

 leaf, the wavy or sinuate margin 

 of the Oak, the irregularly toothed 

 edge of the Dandelion, the spiny 

 margin of the Holly, and various 

 other types of leaf margins. 



Very frequently the margin of 

 the leaf is deeply indented, and 

 if the indentations are regularly 

 arranged, and are so deep as to 

 reach the midrib, a compound 

 leaf composed of a series of leaflets 

 is produced. This will be pinnate 

 or palmate, according to the ar- 

 rangement of the main veins (Fig. 

 47), for the incisions will naturally 

 fall between these. 



Compare the simple leaves of the Ivy and the Beech, both of 

 which are of the net-veined type. Note that in the former the 

 principal veins all radiate from one point at the base, while in 

 the latter they branch off from the midrib almost throughout its 

 length. Now since a compound leaf is produced by the division 

 of the lamina between the principal veins, it is easy to see that the 

 former, so divided, would produce a compound leaf with radiating 

 leaflets. Such an arrangement of veins is termed palmate venation, 

 and the leaves, both simple and compound, more or less divided in 

 this fashion, are called palmate leaves. The arrangement of veins in 

 the second instance is called pinnate venation, and by the incision of 

 the lamina a pinnate leaf is produced, which, in the case of the com- 

 pound leaf, would have opposite leaflets. 



A compound leaf is easily distinguished, even by beginners, from 

 a branch bearing leaves because of the absence of any apical bud or 

 growing point, and by the fact that a bud occurs in "the axil of 

 the main petiole, whereas there are no buds in the axils of the 

 leaflets. 



PINMATE 



Fig. 47. Formation of Palmate and Pin- 

 nate Compound Leaves by the gradually 

 increasing incision of Lammas with Pal- 

 mate and Pinnate Venation respectively. 



169. Leaf -Arrangement. Observations should also be made of 

 the different ways in which the leaves are arranged on the stem. 

 There are two ways in which leaves are arranged alternate (one leaf 

 arising at each "node," i.e. the leaves coming off sinyly from the stem) 

 and whorled (two leaves, rarely more, arising at each node). 



The simplest type of alternate arrangement is that seen in the 

 Broad Bean and in Grasses, where the leaves come off alternately from 

 opposite sides of the stem, so as to form two rows ; this is called the \ 

 arrangement, because each leaf is separated from the next above and 



