2 BULLETIN 223, U. S. DEPARTMENT OF AGRICULTURE. 



To enable the observer to make such foliage comparisons in a pre- 

 cise and systematic manner, capable of tabulation for future refer- 

 ence, is the most important use to which this study of date-foliage 

 characters can be put. 



Most of the workers in the date gardens of the Department of Agri- 

 culture soon learn to recognize the more prominent varieties by such 

 obvious characters as a slender or a heavy trunk; leaves with broad 

 or narrow rib bases, erect and rigid in growth or more or less spread- 

 ing, feathery, and graceful. Less elementary characters are recog- 

 nized, but not formulated, which would distinguish two varieties which 

 might agree in the more fundamental points. There are differences 

 in the broad outlines of the leaf blade as a whole and differences in the 

 blade, as to whether it is smooth and nearly flat or whether from 

 varying angles of the pinna? it appears on the defensive with bayonet- 

 like points thrust out in all directions, as if to resist assault. 



Most persons who become familiar with date trees will distinguish 

 between trees of varieties which possess many characters in common 

 if they are side by side for comparison; fewer will be able to keep the 

 resemblances and differences in mind if the compared trees are on 

 opposite sides of the garden, and a still smaller number will be able to 

 keep varietal characters clearly in mind in going from one locality to 

 another. 



The object of this study has been to determine just what varietal 

 characters in date trees consist in ; then to apply names and formulate 

 these so that they may be used in classifying and determining varieties, 

 much as floral and foliage characters are used by the systematic 

 botanist. 



Perhaps of all cultivated plants the date palm is the most mechan- 

 ical or geometrical in its external structure. The cylindrical, col- 

 umnar trunk has the overlapping leaf bases, like inverted tiles, 

 arranged in broad right or left spirals. The rachis, or rib, is long, 

 smooth, and rodlike, and its expansion toward the base is along 

 symmetrically molded surfaces. 



The leaflets, or pinnae, are in symmetrical ranks from either side of 

 the rib, and each individual has its polished sword-shaped blade folded 

 lengthwise with the precision of machine work. In the unopened leaf 

 the pinnae are placed with the compactness of the ribs of a fan, and in 

 expanding each assumes within certain limits a definite angle with 

 the rachis peculiar to its class. 



Having such features to deal with, the writer feels that no further 

 explanation is needed for the very mechanical way in which the sub- 

 ject of date- tree characters is treated. It is the only method by 

 which the subject can be approached. 



