4 BULLETIN 223, U. S. DEPARTMENT OP AGEICULTUEE. 



The axis of this blade is a stout polished rib, technically called 

 the rachis, which may be several inches broad where the leaf is 

 attached to the trunk, but tapers to a slender tip of less than a 

 quarter of an inch. (See Plate I.) As the leaves are placed on the 

 trunk the face of the leaf, which is inward or toward the center of 

 the tree, may be called the ventral surface. The reverse of this, 

 away from the tree, is the dorsal surface. The right and left sides 

 will be designated with the leaf in a vertical position and with the 

 observer facing the trunk. 



If an entire old leaf is cut away at its attachment to the trunk it 

 will be found that the thick, wedge-shaped base shows torn and 

 ragged margins, or perhaps a bit of matted fiber still clinging to it, 

 where the fibrous sheath has been torn away. At the line of attach- 

 ment sheets of this fiber encircle the tree. If a date palm be dis- 

 sected, cutting away leaf after leaf till we get toward the bud, we find 

 leaves with their original structure entire and the margins of the wide 

 base of the rib thinning out to a continuous mat of brown fibers, which 

 forms a complete sheath encircling all the younger growth. As the 

 area of active growth is approached, near the center this sheath will 

 be yellowish white, soft, and succulent, not more than 2 or 3 inches 

 in diameter, and 8 inches or a foot in length. In a large tree the 

 sheath may be 20 inches or more in length. On the opposite side 

 from the rachis the margin of the sheath has an upward expansion 

 into a broad lingua, or tongue, with coarsely incised margins and a 

 blunt-pointed or an acuminate apex, which sometimes protrudes 

 several inches against the inclosed leaves and which varies in a manner 

 somewhat characteristic of different varieties. The diagonal arrange- 

 ment of the fibers allows the sheath to expand a good deal, but the 

 continual pushing upward of new leaves from within and the expan- 

 sion of the trunk finally rupture it or tear it loose from the sides of the 

 rib. Its lower margin remains attached to the trunk, so that this 

 wrapping of old sheath fiber may persist for many years. In rare 

 instances, the variety Lagoo, for example, the sheath has ear-shaped 

 or auriculate expansions at the upper margin of its attachment to 

 the rachis. Figure 1 shows a typical date leaf with the various parts. 



An entire leaf comprises the upper expanded portion, properly 

 called the blade, which includes the length from the first spines to the 

 top, and the lower portion, representing the petiole, including the 

 broad, wedge-shaped base of the rachis and the sheath. The blade 

 is divided into the spine area and the pinnee area, the exact separation 

 of which sometimes can be only approximated. Varieties differ 

 greatly in the proportion of the leaf blade occupied by the spines, 

 which may range from 18 or 20 per cent to 45 per cent of the entire 

 blade length. 



