CHARACTERS OF THE LEAVES OF THE DATE PALM. 7 



tant factors in determining the form assumed by the tree top that it 

 has been thought worth while to make outline tracings of the cross 

 sections of the rachis of leaves of the different varieties, four series of 

 which are reproduced with the descriptions of the respective varieties 

 as text figures in this bulletin. (See figs. 11, 13, 14, and 15.) The 

 first section is in all cases made just below the lowest spines; that is, 

 at the base of what has been defined as the blade of the leaf, the others 

 1 or 2 feet apart to the apex or near it. 



THE PINNAE. 



The organs commonly called leaflets, or properly pinnae, of the date 

 leaf, including those suppressed as spines, number from 50 or 60 to 

 130 on each side of the rachis. The two sides of the leaf are fairly 

 symmetrical as to the length of the pinnae blades and the angles at 

 which they are placed with the rachis, but not quite symmetricalin 

 numbers, there sometimes being a difference of four or five pinnae on 

 opposite sides of the leaf. While the occurrence of pinnae in pairs 

 is not infrequent, it appears to be largely accidental, and with the 

 general irregularity of their positions they can not be regarded as 

 being paired and opposite in position in the sense in which the mem- 

 bers of many compound leaves are so recorded. 



The pinnae are borne on the lateral faces of the rachis, with normally 

 a single pinna at the apex. In Plates I and IV the terminal pinnae 

 show very plainly on a number of leaves. 



On the lower part of the blade the leaflike pinnae are replaced by 

 stiff acute spines, from 1 inch to 7 or 8 inches in length. These are 

 really modified pinnae, as is clearly shown by the channel in one side 

 corresponding to the fold of the pinnae blade; also by their mode of 

 attachment and arrangement in groups. The larger spines pass by 

 gradations into stiff spinelike forms, which will be called spike pinnae. 

 Above these there are in some varieties extra long, narrow forms, 

 so thin and weak as to be pendulous, which will be referred to in 

 descriptions as ribbon pinnae. In Plate IV the long, pendulous ribbon 

 pinnae can be noticed on the lower portion of several leaves. 



Each pinna consists of a green, leathery, sword-shaped or ensiform 

 blade, folded lengthwise, and a cushiony expansion or callus, called 

 the pulvinus, by which it is attached to the rachis. 



In a few varieties the lower pinnae and some spines do not immedi- 

 ately broaden beyond the pulvinus into the thin blade, but have a 

 short, solid, necklike portion, elliptical in cross section, for which 

 the name collum (Latin for "neck") is proposed. 



Toward the upper end of the leaf in certain varieties the folds of 



the pinnae blade are somewhat unequal, the lower or proximal fold 



being a little broader than the upper one. Instead of being inserted 



directly into the rachis it is attached along the side, running down- 



87664°— Bull. 223—15—2 



