THE VEGETATIVE ORGANS COMPARED = 339 
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 blade, al- 
though it may be 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 
Fic. 293.—Meadow Rue (Thalictrum flavum, Crowfoot Family, Ranuncu- 
lacee). A, flower-cluster. B, flower, enlarged. C, same, cut vertically. 
D, floral diagram. EE, 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.1 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 decompownd. Since in 
1 Pet’-i-o-lule < L. petiolulus, diminutive of petiolus, petiole. 
