126 Bulletin Jard. Bot. Buitenzorg, Série III, Vol. V. Livr. 2, 



As the leaf begins to grow in length the sheath to-gether with the pétiole 

 push their way above the older leaves so that ultimately the top of 

 the sheath is exposed and very soon thereafter begins to die and discolor 

 beginning at the top and continuing gradiially downwards. The ends be- 

 come frayed out; the bast fibres held together inore or less in strands 

 give a ragged appearance to the sheath. The sheath shown in Figure 43, 

 Plate VI is from a tvvo year old plant. Several of the leaves hâve been 

 removed as well as the felt to bring into prominence the sheath. The dark 

 areas represent that part of the sheath tissue vvhich has died and has 

 become tough and leathery. The layer facing the inside which has not 

 been so greatly exposed persists in a living condition for a longer time. 

 From the pétiole of the leaf, to the right of Figure 43, the bast strands 

 are seen emerging from the edges. Thèse bast strands, however, corne 

 from thèse that run parallel upwards in the pétiole and émerge from the 

 pétiole at différent levels. In the maturer leaf vvhere lignification has already 

 occured they appear as a séries of strongly developed saw teeth on either 

 side of the pétiole and always below the last pair of leaflets. Ultimately, 

 due to the death of the enveloping leaves above the sheath it reachès the 

 outside where its tissue dies completely and it persists for a long time 

 lending support to the base of the leaf and thus aiding the leaf to with- 

 stand the severest strains. 



Maturation of the leaf. 



The processes of differentiation within the leaf beyond the formation 

 of the leaflets and the young stages of the sheath, rachis, pétiole and base, 

 hâve not been embraced in the scope of the présent work and no attempt 

 has been made to view the steps in the light of the immense amount of 

 work that has been done on palms as well as on other plant groups. 



For the discussion of the spécial organs at the base of each leaflet 

 which détermine the position of each leaflet with référence to the rachis 

 attention is called to the observations of RuDOLPH (-^) "Zur Kenntnis 

 der Entfaltungseinrichtungen an Palmenblattern". Thèse organs (Polster) 

 reach their maximum development after the leaf has emerged and has 

 completely unfolded. The leaflets at the base of the leaf, abort in 

 varying numbers, soon after the émergence of the leaf. The leaflet biade 

 drops off and the mid-rib persists in the form of a sharp stout spine 

 imbedded in this 'Polster'. Thèse spines together with the saw teeth of 

 the pétiole (of quite a différent origin) give an armed appearance to the leaf. 



Lignification proceeds from the tip of the leaf downwards. If oiie 

 examines a leaf that is emerging in the form of a spike one finds lignifi- 

 cation of the rachis beginning at the tip and if one follows the leaf down 

 to the pétiole and base, which hâve not yet emerged, the tissue is still very 

 tender and pliable, not résistant and very easily eut through with a knife. 



