THE 



5 



The broad outlines of the blade vary considerably with different 

 varieties and are determined 



by the length of the pinnae 



in different parts of the blade 



and the angles which they 



form with th e rachis and 



plane. To illustrate: If in a 



given leaf the pinnae at the 



middle of the blade are 16 

 inches long and placed at 



right angles, or 90°, with the 

 rachis and lie in the plane of 

 the blade; that is, so that 

 the leaf is flat, the leaf will 

 be 32 inches broad, not count- 

 ing the breadth of the rachis 

 fig. 2, A, Ih). Let the same 

 length of pinnse be placed in- 

 clined only 45° from the 

 rachis and still in the plane 

 of the blade, then the blade 

 will be but 22f inches broad 

 (fig. 2, A, cc). But let the 

 pinna?, instead of lying flat 

 (fig. 2jBy h) diverge 45° from 

 the plane of the blade, as well 

 as 45° from the rachis (fig. 2, 

 Bj c)y then the leaf blade be- 

 comes a V-shaped trough only 

 16 inches broad, or half the 

 breadth of the blade with the 

 pinnae flat and at right an- 

 gles- 



THE RACHIS, 



A close inspection of the 

 rachis of the date leaf shows 

 that it is irregularly four- 

 sided; the inner or ventral 

 surface is usually strongly 

 arched or at the first spines 

 is made up of two ogee curves 

 turned together. The back 

 or dorsal surface is moder- 

 ately or often strongly 

 rounded at the base, slightly rounded or rarely flattened toward the 



Fig. 1. — A typical date leaf, showing its various parts. 



