30 M.Tt€cVi\ on the Structure of the Leaves of Palms. 



fibrous thread which runs along the whole length of the leaf, and 

 retains the leaflets in union for some time after their expansion. 

 This filament and the brown pellicles which cover the leaves at 

 this period have a similar origin. They arise from an envelope, 

 within which the leaflets are organized, and which becomes dried 

 up and falls in small brown flakes. The existence of this enve- 

 lope may be recognized in the very young leaves, even at the 

 period when the furrows (as in the Chamadored) begin to make 

 their appearance. The leaflets then appear to be formed in a 

 substance of a gelatinous appearance, Avhich is the origin of this 

 pellicle. 



The leaflets of all palms are not plaited in the same direction ; 

 some, as Chamadorea Martiana, Ceroxylon andicola, Areca rubra, 

 Arenya saccharifera, &c., have them folded on the lower surface ; 

 others, in which the scission is carried to the ridges of the inner 

 surface and not to those of the outer, have the leaflets folded on 

 the inner surface, as Phoenix dactylifera, sylvestris, Fulchiron se- 

 negalensis, kc. There are other palms of which the leaflets are 

 broader and contain several folds of the primary lamina. It ap- 

 pears to me that very good characters may be derived from the 

 plication of the leaflets. 



The limb of the simple leaf of Geonoma baculum is somewhat 

 differently developed ; the rachis emits a lanceolate limb, widest 

 at the base ; this becomes plaited first at this basal portion, the 

 folds extend in proportion to the growth of the leaf, and the 

 upper extremity becomes cleft to form the two terminal lobes. 



In Chamcerops humilis, as in Chamcedorea and plants with 

 sheathing leaves, all the leaves are enclosed by their sheaths. 

 In a leaf of 1 millimetre the sheath was equal to the half of the 

 length of the leaf ; it was opposite to an inflated portion covered 

 with hairs, which is only the rudimentary lim-\ I removed all 

 these hairs and with them a pellicle which clothed this part of 

 the leaf. In this manner I arrived at a rounded surface, di\dded 

 longitudinally into parallel ribs on the anterior and posterior 

 surfaces of the limb. The surface being convex, the ribs are 

 shorter on the sides than towards the middle. They are inserted 

 on a nearly horizontal plane and rise parallel in gromng. Each 

 rib of the outer surface corresponds to the median nervure of a 

 lobe of the leaf. 



As long as the leaf remains enclosed in the sheath, all its parts 

 consist of a very delicate tissue, but as soon as its apex reaches 

 the air and light it becomes green, grows rapidlj', and acquires 

 consistence ; the limb is often hard and coriaceous and contains 

 much woody matter, whilst the base of the petiole, which is en- 

 closed in the sheath, is still of extreme fragility. It is also this 

 lower portion which continues growing longest. Thus the limb 



