THE VEGETATIVE ORGANS COMPARED 330 



All the leaves so far considered agree in having the blade 

 of a single piece however much it may be branched or sub- 

 divided. That is to say, the green pulp of the ])lade, al- 

 though it may l)e but little developed between the ribs, is 

 still continuous. Such are called simple leaves. When the 

 green pulp is discontinuous between the ribs, as in the leaves 

 of the Christmas rose, the blade becomes divided into second- 

 ary blades or leaflets, each of which may be borne on a little 



B Do «' 'S's-u, ! 



Fig. 293. — Meadow Rue {Thulictrum flavum, Crowfoot Family, Raniincu' 

 lacece). A, flower-cluster. B, flower, enlarged. C, same, cut vertically. 

 D, floral diagram. E, pistils. F, fruit, entire, and cut vertically. 

 G, seed. (LeMaout and Decaisne.) — -Perennial herb about 1 m. tall; 

 flowers yellow; fruit dry. Native home, Eurasia. 



stalk of its own, called a petiolule^ Such leaves are classed as 

 divided or compound. If, as in this example, the leaflets or 

 their petiolules spring directly from the main petiole the leaf 

 is distinguished as once-compound; when, as in baneberries, 

 the branching of the blade is carried a stage farther and 

 the leaflets or their petiolules arise from branches of the 

 petiole, the leaf becomes twice-compound; or the subdivision 

 may be carried still farther, as in columbines. A leaf more 

 than once compounded is termed decompound. Since in 

 ^ Pet'-i-o-lule < L. petiolulua, diminutive of petiolu>i, petiole. 



