THE LEAF. 



173 



Celakovsky describes abnormal inflorescences of the 

 hornbeam (Carpinus Betulus) in which the two brac- 

 teoles, normally fused laterally with the bract, were 

 quite free (fig. 48, a-d). Both this and the above- 

 cited cases of stipules are obviously reversions to a 

 primitive condition. 



Conclusions on Leaf-division. — Apart from those 

 few cases of leaf-division which may be attributed 

 to depauperization and leaf-forking in Angiosperms, 

 the phenomenon should be regarded as entirely a 

 reversionary one, i. e. a modification in the direction of 

 an ancestral character. We find in fact that simpli- 

 fication or reduction has played snch a large part in 

 the evolution of plant-life that abnormal tendencies in 

 the opposite direction seem to be best interpreted as 

 reminiscences (to nse a Platonic word) of features 

 long left behind. In other words, compound leaves 

 are to be regarded as more primitive than simple 

 leaves. Most botanists would hold that the simple 

 leaves of certain Leguminosse, e. g. Rafnia, Podalyria, 

 Borbonia, and Judas-tree (Gercis) have been derived 

 from simplification and reduction from ancestors with 

 compound leaves, seeing that these are typical of the 

 vast majority of Leguminous plants, and few would 

 deny that the leaves of the pennywort (Hydvocotyle 

 vulgaris) and the hare's-ear {Bwpleurum) are modified 

 and more recent in type than those of the vast majority 

 of Umbelliferas. 



The two types of reversion which we meet with 

 are : (1) an increase in complexity of the leaf, and 

 (2) an increase in number of the leaves. Such cases 

 as those of simple leaves becoming compound come 

 under (1) ; for reasons which will appear later all 

 cases of dichotomy are preferably placed under (2). 

 The multifold dichotomy of leaves, e. g. those of ferns, 

 known as " cresting," may be regarded as a case of 

 fasciation, of precisely the same nature as that met 

 with in the stem, where we also find all transitions 

 between simple dichotomy and typical fasciation. 



