LEAVES 



7 



•5^ 



1 



t 



t 



determining 



has been thought worth while to make outhne 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 lojvest 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 PINN^. 



The organs commonly called leaflets, or properly pinnsD, 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 pinnte blades and the angles at 

 which they are placed with the rachis, but not quite symmetrical in 

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

 opposite sides of the leaf. While the occurrence of pinna3 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 pinnse are borne on the lateral faces of the rachis, with normally 

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

 show very plainly on a number of leaves. 



On the lower part of the blade the leaflike pinna3 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 pinnoe blade; also by their mode of 

 attachment and arrangement in groups. The larger spines pass by 

 gradations into stiff spinehke forms, which wiU bo called spike pinnse. 

 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 pimiae. 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-shapcd or cnsiform 

 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 piim^e and some spiiu^s do not immedi- 

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

 short, sohd, 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 behig inserted 

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



87664"*— Bull. 22J— 15 2 ' 



