YAMPQLSKY : Study of OU palm. 1^1 



VON MOHL and later Naumann lay sucli i^reat stress iipoii. To this 

 we shall returii in our gênerai discussion. This tissue on the sides of tlie 

 leaf witli the slits torn into it, however, persists both on the outer and 

 inner surfaces of tlie leaf adhering to the sides of the leaflet. 



The sac-iike cliaracter of the leaflet is soon lost as a resuit of the 

 mutual pressure of the leaflets so that the sides. of the sac approxiniate 

 each other and lie closely pressed against each other much in the manner 

 of a flattened out paper bag. Altération in forni is now due to growth in 

 length, to pressure, to stretching and to differentiation that goes on within 

 the leaflet itself. The varions forms that the leaflet takes on are shown in 

 séquence in Figures 16, 17, 19, 20, 21, 18, 15, 13, and 14, Plate 11. One 

 can readily pièce together the history of the leafiet from the varions aspects. 



Figure 15 is a portion of a leaf of a two year old plant in the same 

 stage of development as the leaf shown in Figure 14. It brings out very 

 strikingly the fate of the strip of tissue which until final unfolding of the 

 whole leaf holds the leaflets together. 



It is difficult, at first, to visualize the process and 1 hâve found it best 

 in an effort to get a clear picture of the steps that lead up to that structure, 

 to bear in mind a mechanical contrivance which most closely approaches 

 the relation of the leaflets and the strip which holds their apices together. 

 This strip may be compared with the rod which holds the horizontal slats 

 of a wooden shutter together and which, when shoved up or down, causes 

 a synchronous movement of the slats. If instead of the wooden slats we 

 replace them in our minds by triangular leaflets attached to the rhachis 

 and we further replace the strip that holds the slats together, by the 

 strip of tissue of the leaf blade, then we can readily visualize the rela- 

 tionship of parts in the leaf blade. And if further we can conceive that a pull 

 exerted at the top of such a mechanism would stretch the undifferentiated 

 strip much more than the leaflets which hâve during their differentiation been 

 reinforced by the tissue developing within them, we hâve a fairly true picture 

 of what happens to the undifferentiated strip which is subjected to the pull 

 developed by the upward growing leaflets. 



By carefully dissecting out the leaves, thèse prolongations (Figures 15, S, 

 Plate II) can be readily recognized — they are the remains of the enveloping 

 strip under discussion. Thèse prolongations persist and at the unfolding of 

 the leaf they are the last to separate so that for a time the leaflets, held 

 together by their tips, appear to hâve been stamped out of a whole pièce, 

 the periphery of the leaf representing the remuants of the whole leaf blade. 



The tips of the leaflets are made up of two distinct tissues — the tissue of 

 the leaflet proper and the remains of the strip. This tip does not persist 

 but dries up and falls off. 



The rest of the enveloping tissue — the tissue that formerly surrounded 

 the leaflets — persists until the leaf is ready to unfold. This tissue can be 

 readily recognized because of its large cells. In dissecting out the leaflets it 



