CHARACTEES OF THE LEAVES OF THE DATE PALM, 



11 



the trouglij or valley, of the blade, the rib being on a level with the 

 eye. The 6-ranked leaves have a ragged and aggressive appearance, 

 and with their formidable thorns and acute pinna tips are most com- 

 pletely armed against predatory animals. 



Examining the pinnse of the three classes — antrorse, introrse, and 

 retrorse — we find that each has its well-defined relative position of 



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I 



V 



a 



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7 



I 



e 



I 



I 



r* 



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I 



a 



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4 



a 



3 



2 



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A 



B 



C 



D 



E 



Fig. 5.— Sections of date leaves. A , An Areshti leaf. On the L side of the racliis is shown a triple group 

 of pinnae (a, j,r) and above it a paired group {a,ry, on the R side, a paired group (a, r) below and a triple 

 group (a, f, r) above. B, Section toward the top of a Deglet Beida leaf, view of right side. Below is a 

 triple group of pinniB (a, t, r); above, a quadruple group (a, i, J, r). C, A Deglet Beida leaf, showing on 

 the left-hand side of the rachis a quintuple group of pinnas (a, /, /, i, r). The pulrinus of the s^trorse 

 pinna (a) is caudate, having a tail-like prolongation reaching nearly to the next lower pinna. D, Section 

 near the apex of an Areshti leaf, in which the pinnae are not distinguishable into groups, though Nos. 1, 

 4, and 7 are slightly retrorse in position. E, A Deglet Beida leaf, showing pulvini of aiitrorse pinnae: a, 

 a, Caudate; a, f, r, coalescent with the groups above and below by these prolonged pulvini. 



divergence from the midrib, or rachis, measured by its angles of 

 divergence from the imaginary leaf planes. The antrorse pinnae 

 diverge least from the plane of the rachis, pointing strongly forward, 

 and their two ranks most nearly approach each other, thus forming 

 the greatest angle with the plane of the blade. The introrse pinnse 

 are placed most nearly at right angles with the plane of the rachis, 

 or rib, and more nearly to the plane of the blade than the antrorse* 



The retrorse piiuise generally point far fonvard, then* divergence 

 from the plane of the rachis being slightly greater than that of the 



