6 



BULLETIN 223^ U. S. DEPARTMENT OF AGRICULTURE. 



top. The sides or lateral faces are flat or somewhat concave, and 



their inner margins, at first slightly converging, as they approach the 



top are drawn so near together as to give a triangular cross section 

 to the rib. 



The characteristic form or habit of tree tops of each date variety, 

 due to the curves of the leaf blades, is largely determined by the 



flexibility of the 

 rachis. This is gov- 

 erned in part by the 

 degree of firmness and 

 elasticity of the fiber 

 of the rachis, but 

 more by the way in 

 which the diameter 

 diminishes along the 

 different faces. 



The feathery grace 

 of the Areshti variety 

 is due to the leaves 

 maintaining consider- 

 able rigidity in the 

 lower portion, but 

 \ with the rachis di- 



\ minishing to a deli- 



— "V ^^^^ ^^^ slender flexi- 



'v* bility at the apex. 



— HI) 1^]^^ broad, open top 



I and loose, lazy curves 



of the Rhars leaves are 



{ 



3 



i 







. due to a rather rapid 

 diminishing in the di- 



FiG. 2.— Diagram showing how the size of the date leaf is affected by amcter of the rachlS R 

 the angles which the pinrise form with the rachis. A represents the ghort distaUCO abo Ve 

 leaf as lying flat, the dotted lines (6 &) showing the breadth the leaf .i r . • 



would have with the pinnae at 90=^ of axial divergence, the solid lines the DaSC, yet mam 

 (c c) showing the breadth of the leaf with pinnse diverging 45** from 

 the axis, B represents a cross-section view of the leaf, 6 showing the 

 pinnffi lying in the blade plane, or flat, but with an axial divergence 



of -45"; c shows the same pinna* also diverging 45** from the blade 

 plane, 



ness. In the Thoory 

 1 other varieties of that class the thick, strong rachis holds its size 



^ much 

 in the apical portion 

 to give grace or airi- 



and o 



the growth of the inner leaves. 



rving only 



uncom 



promising aspect through the entire top. 



The relative size and form of the rachis in different portions of the 

 blade are so characteristic in the different varieties and such impor- 



f 



