CHARACTERS OF THE LEAVES OF THE DATE PALM. 9 



+ 



It is not to be supposed that date leaves are so perfectly laid off 

 along geometric lines that we have bnt to read a set of angles, refer 

 to a table, and say with confidence, '^this is Thoory/' or '^this is 

 Hay any," But it is true that certain ranges of angles are found 

 only in certain varieties, and, along with other characters, are impor- 

 tant factors in identification. 



PINN^ CLASSES 



A third character in the insertion of the pinnse remains. In aU 

 species of the genus Phoenix the folded pinnse are attached to the 

 rachis, with the margins and channel inward, or toward the ventral 

 face of the leaf, and in some species, as Phoenix canariensisy they are 

 quite uniformly attached with the channel directly inward, or at 

 right angles with the blade plane. 



In the date palm^ while all the pinnae face generally inward, or 

 ventrally, only a portion of them face directly inward or at right 

 angles to the blade plane. An important class of them are placed 

 facing obliquely forward or upward, and about an equal number 

 face obliquely backward or downward, thus giving three distinct 

 classes of pinnae as to position. 



Those with the fold facing directly inward, or attached at right 

 angles with the rib, will be called introrse,' using a botanical term 

 meaning ^ ^ directed inward.'' 



A second class includes pinnae with the channel directed obliquely 

 upward, or toward the apex of the leaf, and for these the term 

 antrorse,^ meaning '* directed upward or higher,'' will be used. 



In a third class the pinnae have the channel directed more or less 

 obliquely, downward, or toward the base of the leaf, and the term 



r 



retrorse,^ meaning ^'directed back or downward," will be applied 

 to these. 



PINN^ GROUPS. 



4 



Studying the pinnae along the side of a leaf, we soon notice that 

 these classes of pinnae are not placed at random, but that there is a 

 regularity in then- succession. In other words, the pinna3 along the 

 respective sides of the rachis are arranged in groups of two, three, 

 four, or, rarely, five, a group of two being the most common. These 

 groups fall into regular and irregular classes. The regular groups, 

 which constitute the normal or regular form of aiTangemcnt, consist 

 of a lower or proximal antrorse pinna and an upper or distal retrorse 

 pinna, between which may occur one, two, or, rarely, three introrse 

 pinnae. Figure 4 shows the ventral surface and left side of a section 

 of a rachis with the pinnae cut to about an inch loner- There are 



1 "Introrse, introfsm (Mod. Lat.)i turned inward, toward the axis." 



s '*Antrorse, antrofsus (antero-, before, versus, turned toward), directed upward, opposed to retrorse." 

 •"Retrorse, retTofsum (Lat.)i directed backward or downward. "_ (Jackson, A Glossary of Botanical 

 Terms.) 



