48 THE STOKY OF THE PLANTS. 



The two types of rib-arrangement to which I 

 have already called attention exist for the most 

 part in one of the two great groups of flowering 

 plants about which I shall have more to say to 

 you hereafter. There is yet a third type, how- 

 ever, which occurs in the other great group (that 

 of the grasses and lilies), and it is known as the 

 parallel (Fig. 6). In this type, the ribs do not 

 form a radiating network at all, but run straight, 

 or nearly so, through the leaves. Examples of 

 it occur in almost all grasses, and in tulips, 

 daffodils, lily of the valley, and narcissus. Leaves 

 of this sort have seldom any leaf-stalk ; they 

 usually rise straight out of the ground, more or 

 less erect, and their architectural plan is gene- 

 rally quite simple. They are seldom toothed, 

 and hardly ever divided into deeply- cut segments 

 or separate leaflets. 



A few more peculiarities in the shapes of 

 leaves must still be noted, and a few words 

 used in describing them must be explained very 

 briefly. When the leaf consists all of one piece, 

 no matter how much cut up and indented at the 

 edge, it is said to be "simple"; but if it is 

 divided into distinct leaflets (as in Fig. 5), it is 

 called "compound." If the edge is unindented 

 all round (as in Fig. 6), we say the leaf is " en- 

 tire " ; if the ribs form small projections at the 

 edge (as in Fig. 4), we call it " toothed " ; if the 

 divisions are deeper, we say it is "lobed" ; and 

 when the lobes are very deeply cut indeed, we 

 call it "dissected." Thus, in order to describe 

 accurately the shape of a leaf, we need only say 

 which way it is veined or ribbed whether finger- 



