THE LEAF. 



171 



the avens (Geiim), silver-weed (Potentilla anserina), 

 agrimony (Agrimonia Enpatorium), and meadow-sweet 

 ( Spir se a Ulm a via) . 



The leaflets of Trifolkm may not be evenly divided 

 into two; De Vries figures a case in T. praiense in 

 which the terminal leaflets had excised a lateral 

 smaller leaflet on either side. 



Many p innately-leaved ferns, such as the male fern, 

 besides having the tips simply forked, or " crested," 

 may exhibit a similar phenomenon in each of the pinnge 

 (PI. XIV, fig. 1). 



Fig. 47. — Trifolium pratense. a. Leaf with five leaflets, b. Leaf reverted 

 to ancestral pinnate structure, (b. After De Vries.) 



Bifurcation also occurs either in the terminal or 

 lateral leaflets of multifoliolate pinnate leaves, e. g. in 

 the false-acacia (Bobinia Pseudo-acacia) and crown- 

 vetch (Coronilla varia). Now, if complete partition of 

 the leaflet occurs in the terminal leaflet of a compound 

 imparipinnate leaf, a paripinnate leaf, devoid of ter- 

 minal leaflet, would result, e. g. in Robinia and 

 Gleditschia ; and if this occurs in the terminal leaflet of 

 a trifoliolate leaf it would afford a transition between 

 trifoliolate and pinnate leaves, although the former may 

 be regarded as merely a pinnate leaf reduced to one 

 terminal and two lateral leaflets. On the other hand, 

 an unequal division of the terminal leaflet of the nature 



