﻿EXISTING AND FOSSIL CYCADS COMPARED. 



2O0 



THE LEAVES. (Figs. 46-48. and 120-123.) 



The earl\- development of the leaf strongly recalls that of fern fronds. In the 

 young seedlings the vernation of the cotyledons is conduplicate, a condition that 

 is further noted in the staminate fronds of the Cycadeoidese and the rachis of the 

 Zamia fronds. The young leaf first appears at the apex of the trunk as a low 

 and rounded hillock. Lateral wing-like expansions soon form at the base, and, as 

 the frond becomes more conical in shape and a few millimeters in height, pro- 

 long themselves as low and rounded ridges running out along each side of the 



middle portion or rachis. And on these 

 ridges, as represented in figure 121, about 

 the time the frond reaches a length of from 

 2 to 4 mm., the young pinnules begin to 

 appear as rounded protuberances. In most 

 cases the order of appearance is basipetal 

 (from apex to base), as in the examined 

 species of Encephalartos, Macrozamia, Ccra- 

 tosamia, and Zamia. In Dion the order is 

 mostly basipetal, but it seems in part acro- 

 petal (or ascending) at the apex. In Cycas 

 Jenkinsoniana the order is divergent from 

 about the middle of the fronds, and in C. 

 Seemanni it is a mixed one. It is to be 

 borne in mind that these statements refer to 

 such stages as are shown in the text-figures. 

 The scale leaves are at first similar to the 

 foliage leaves, except that they possess fewer 

 pinnules, which soon abort. But while the 

 lateral petiolar thorns of Cycas Jenkinsoniana^ 

 etc., are known to be aborted pinnules, those 

 of Ceratozamia and various other forms are 

 of an ordinary thorny distribution and 

 character. By the time the entire frond 

 has reached a length about equal to the 

 thickness of the armor and is ready to 



( 1) Stangeria paradoxa seedling bearing the first (oliage emerge by the final rapid stage of growth, all 

 leaf (1) the radical (r). and the cotyledons (c) em- the parts and the bundle systems are quite 



bedded in the megasporangium. (Alter Worsdell.) 1 



(2) Oak seedling, showing hypogaeous germination of perfectly formed. But as a rule the pin- 

 a dicotyl. (From Gray.) nules are relatively much larger and more 



completely grown at this stage in such cycads as Dion and Encephalartos, which 

 have very hard and bristly fronds, though iu Macrozamia spiralis the acuminate 

 but easily curling pinnules also reach a nearly full size before the rachis markedly 

 elongates. In other cycads with soft or leathery leaves, as Cycas, Zamia fiori- 

 dana, and Stangeria the pinnules are more backward in forming. But there is 

 every gradation between these two extremes, so that cycad fronds vary very greatly 



