80 THE PALM-STEM : 



other and become free ; when, on the other hand, I ex- 

 plained this tissue as a peculiar form of the pubescence, 

 I was wrong, as the following observations will show. 

 I traced the development of the leaf in Pkcenisc (pi. I, 

 figs. 9-13) and Co cos fleocuosa (figs. 1-8) ; in both, the 

 young leaflets (figs. 1, 12, 13), until they attain the 

 length of about five millimeters, are composed of a con- 

 nected tissue, which in the middle, as rudiment of the 

 future petiole, is thicker, and runs out into a relatively 

 thin border at each side. At a later period a smooth 

 furrow is formed between the thickened mid-rib and the 

 margin of the leaf (fig. 2), at the bottom of which are 

 subsequently met with, nearly approached, somewhat 

 excavated cross-striae (figs. 3, 4), the tissue of the leaf, 

 however, being still continuous. These cross-striae are 

 afterwards converted into narrow slits (figs. 5-11), which 

 in Cocos flexuosa penetrate the entire thickness of the 

 leaf, so that they are visible on the upper and lower sur- 

 faces (fig. 7 o). The further development shows that the 

 part lying between each pair of slits becomes perfected 

 into a leaflet, and in a cross section (fig. 7 c], or, still 

 better, in a longitudinal section, it is perceived that these 

 pinnae are folded together, and that the mid-rib, at which 

 the fold takes place, is in Cocos on the upper surface, so 

 that consequently twice as many slits are visible at the 

 under side of the leaf as at the upper (fig. 7 c). The 

 margin of the leaf, at which the points of all the pinnae 

 are blended, forms a continuous cellular mass, which ends 

 externally (fig. 8*) in an acute angle (the border of the 

 previously undivided leaf). With the advance of the 

 development of the leaf this cellular mass dries up, and 

 is thrown off in the form of a brown filament, by which 

 the leaflets are set free. In Phoenix (figs. 9-13) the 

 matter is rather different, as the mid-rib of the leaflets is 

 turned toward the under side of the leaf, and the cellular 

 mass which connects the pinnae is not merely blended 

 with their summits, but is continued over the whole of 

 the upper surface of the leaf as a rather thick membrane, 



