10 



BULLETIN 223, U. S. DEPARTMENT OF AGRICULTURE. 



four paired groups in succession, each of an antrorse pinna (a) and a 

 retrorse pinna (r). 



Figure 5, A, shows a ventral view of a section of a leaf, on the 

 left side (L) of which, from below upward, is a triple group (a, i, r) 

 and a paired group (a, r). On the opposite side (R) is a paired group 

 below and a triple group above. 



In figure 5, B, the right-hand side of a section cut well toward the 

 top of the leaf shows a triple group below and a quadruple group 

 above. It should be noted that the antrorse and retrorse pinnae are 

 not placed as obliquely as in those near the base of the blade. 



In figure 5, C y the left-hand side of a section in about the middle of 

 the blade shows a group of five pinnae (a, i, i, i, r). This group is 

 found in comparatively few varieties and only in small numbers. 



Thus, there are four kinds of these regular groups. Noting them 

 by the initial letters of the component pinnae, they are, first, the 



Fig. 4. — Section of a date leaf, showing the rachis and the bases of four paired groups of pinnae, each group 

 comprising an antrorse pinna (o) and a retrorse pinna (r). 



simplest and most common paired group of an antrorse and a retrorse 

 pinna (expressed as a, r) ; the triple group, with one intermediate 

 introrse pinna (expressed a, i, r) ; the quadruple group, including 

 two introrse pinnae (a, i, i, r) ; and the quintuple {a, i, i, i, r). 



Of irregular groups of pinnae there is a great variety — a, i; a, i, i; 

 a, a, r; a, r, r; a, i, a, r, etc. Often toward the apex of the blade the 

 groups become obscured and the classes not well defined, merging 

 into introrse pinnae. In some varieties there is, especially toward 

 the apex of the blade, a decided uniformity in leaflet insertion, the 

 antrorse and retrorse pinnae nearly disappear, and the groups are 

 not well defined. 



Figure 5, D, shows the left side of a section from a leaf of Areshti, cut 

 near the top. Here no definite grouping could be made. The first, 

 fourth, fifth, and seventh show a slightly oblique retrorse position, 

 but such an area would be recorded as "indefinite." 



In these the blade has nearly a plane surface, the pinnae falling 

 most nearly into two ranks. Where the grouping is most pro- 

 nounced, six distinct ranks of pinnae can be discerned, three on either 

 side of the rachis. This is best noted by looking from the apex down 



