16 



BULLETIN 223, U. S. DEPARTMENT OF AGRICULTURE. 



rachis into two equal parts, right and left. The ventral face of the 

 rib is shown at V, the dorsal at D. 



It will be noticed that in the illustrations of the use of form B 

 (figs. 8-10), the protractor circle is carried 20 degrees beyond the 

 zero plane toward the dorsal face of the rachis. This is for recording 

 the position of the retrorse class of pinnae, which, while sometimes 



forming angles of a 

 few degrees toward 

 ^ the inner or ventral 



side, as a rule he either 

 at zero or inclined 5°, 

 10°, or even 20° dor- 

 sally. 



APPLICATION OF THE 

 SYSTEM TO THE 

 DEGLET NOOR VA- 

 RIETY AND ITS 

 SEEDLLNGS. 



As the Deglet Noor 

 is the most prominent 

 variety of date yet in- 

 troduced, a more ex- 

 tensive study of its 

 foliage characters 

 has been made than 

 of any other variety. 

 The following are 

 some of the most strik- 

 ing points brought 

 out: 



The average of eight ex- 

 amples of Deglet Noor 

 leaves gives the spine area 

 as 35.5 per cent of the blade 

 length. 



For the same trees the av- 

 erage proportion of pinnae 

 of the different classes, in- 

 cluding spines where the 

 class is evident, to the total number on the blade, is as follows: Antrorse, 38.1 per 

 cent; introrse, 19.4 per cent; retrorse, 34.1 per cent; uncertain, 8.4 per cent. The 

 paired groups of pinnae exceed all the others together. 



A larger number of observations of this variety may establish a somewhat different 

 set of ratios, but these must serve for a working basis till such can be procured. 



As showing the application of such study of the leaves of a given 

 variety and its value in selecting plants for breeding purposes, a com- 



Fig. 9. — Diagrams showing the characteristic divergence of the pinnae 

 of a Deglet Noor date leaf, at 5 to 6 feet from the base of the leaf, 

 recorded on form B. The upper diagram shows the divergence from 

 the blade plane; the lower, the divergence from the apex: A, An- 

 trorse pinna?; /, introrse; R, retrorse. 



