Wall-Rue 29 



in the following case, and vice versa. The leaflets remaining are 

 thus rendered alternate on the rachis. 



Almost coincidently with the formation of this primary rachis, 

 similar development of leaflets upon it into secondary leaflet- 

 bearing rachises is begun (Figs. 5 e, 6 e, and "j eg). This is some- 

 times followed by similar development of leaflets upon the sec- 

 ondary rachises into tertiary leaflet-bearing rachises (Figs. 9 h, 

 10 h'). 



It will be noted that in each instance development of the leaf- 

 lets of each rachis into leaflet-bearing rachises begins with the 

 leaflet lowest (first formed) on that rachis, and involves succes- 

 sively the leaflets above in the order in which they were formed; 

 and that likewise the formation of the tertiary rachises begins on 

 the lowest (first formed) secondary rachises, and involves suc- 

 cessively the secondary rachises above in the order in which they 

 were formed. 



The venation is flabellate. In consequence,* each incision 

 that transforms a leaflet or simple leaf-blade into two leaflets 

 occurs between the vein-branches formed by the first forking of 

 the vein that enters that leaflet or leaf-blade. Each branch thus 

 becomes the vein entering one of the new leaflets; and the first 

 forking of the one entering the leaflet that is in turn to subdivide 

 forms the two branches between which the incision is to occur, 

 while the part of it below its first fork is contained in that leaf- 

 let's base, which finally becomes elongate and forms a section of 

 rachis. Sometimes the subdivision of a new leaflet takes place 

 before it becomes fully separated from the old one, giving the old 

 the appearance of being cut into three. 



When a leaflet on one rachis subdivides in the beginning of 



* See Chapter I, pp. ig and 20. 



