HOW PLANTS EAf. 



45 



roundish leaf like that of the so-called nastur- 

 tium. But if the ribs project a little at the edge 

 in other words, if the cellular tissue does not 

 quite fill out the whole space between them 

 we get a slightly indented leaf, like that of the 

 scarlet geranium or the common mallow. If the 

 unfilled spaces between the ends of the ribs are 

 much greater, then the ribs project into marked 

 points or lobes, and we get a leaf like that of ivy. 



FIG. 3. FEATHER-VEINED LEAVES. The four leaves have 

 similar veins, but are differently filled in. 



Carry the starving of the cellular tissue a little 

 further still, and we have a deeply-indented leaf 

 like that of the castor-oil plant. Finally, let the 

 spaces unfilled go right down to the common 

 centre from which the ribs radiate, and we get a 

 divided or compound leaf, like that of the horse- 

 chestnut, with three, five, or seven separate 

 leaflets. (See Fig. 5, No. 1.) 



Similarly with the feather -veined type (Fig. 3) ; 

 the spaces between the ribs may be more or less 

 filled with cellular tissue in any degree you 



