THE LEAF. 



235 



the branch ; an instance is figured by Klein in Weigelia 

 rosea. Another interesting case of fusion of leaves 

 induced by a change in the leaf-arrangement was 

 observed in Lonicera tJdhetica : of the two whorls 

 already described, the approximation of the two leaves 

 of the uppermost one leaving a wide gap on the oppo- 

 site side indicates that the third member of the whorl 

 of three is missing from this gap, and the forking of one 

 of the two apices resulting from division of a member 

 of the whorl of three of the lower node indicates that 

 the leaf missing from the whorl above has fused 

 laterally with one of the leaves of the lower whorl ; 

 if again separated off it would come to lie immediately 

 under the wide gap occurring in the upper whorl. 



Celakovsky cites an interesting case in Buscus : he 

 noted a transition in the phyllotaxis of the scale-leaves 

 from the normal f to the ^ type which involved the 

 congenital approximation and fusion of two of the 

 leaves to form a double-leaf.* 



Many cases have been cited above of double leavesf 

 which are clearly cases of fusion. Cases of division, 

 however, are seen where one of a pair or group of 

 three cotyledons is forked, or where more than the 

 normal number of cotyledons occur, as in the wall- 

 flower and sycamore. In a seedling of the former 

 plant imperfect splitting of one of the cotyledons took 

 place in such a w T ay that the two laminae so formed 

 were exactly opposed to each other and at right angles 

 to the undivided cotyledon ; in another seedling where 

 both cotyledons were completely doubled, the members 

 of each resulting pair were similarly opposed ; these 



* Delpino, owing- to the fact that he always regarded the phenomenon of 

 double leaves exclusively from the developmental (i. e. ontogenetic) stand- 

 point, and never, as he ought to have done, from the teleological point of 

 view, becomes involved in error when he ascribes " multiplication " as the 

 sole cause in every case of double leaves; he excludes " fusion " as a cause 

 for the reason that it would involve a disturbance of the phyllotaxis. He 

 had evidently never come across such cases as that described by Klein in 

 Weigelia and by the present writer in Lonicera. He also appears to have 

 no conception of the phenomenon of congenital displacement and fusion. 



f This term is used for any leaf showing apical division, no matter what 

 its origin may be. 



