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RELATIONSHIPS. 



The pinnules are commonly inserted in two parallel furrows separated by a 

 broad, heavy, strongly convex midrib. Sometimes the bases are narrow, but there 

 is every variation from narrow to broad based forms, in which the bases fill all the 

 space of the insertion furrow, or even slightly overlap, the posterior basal edge 

 running down beneath the anterior edge of the base of each preceding pinnule, as 

 in Dion and certain species of Cycas. The insertion of pinnules varies from opposite 

 to alternate, often on the same rachis. The rachis may end in a rudimentary point, 

 with the terminal pinnules smaller and smaller, thus producing acuminately tipped 

 fronds {Dion), or the terminal pinnules may be of quite full size and the frond 

 truncate {cf B, fig. 123). The number of pinnules varies from a half dozen to as 

 many as 125 on each side of the midrib. Basally the pinnules degenerate into 

 spines, or fail of development, being, as already noted, abortive. In addition, the 



petiole and rachis of Zamia 

 pseudoparasitica, also Zamia 

 ll'allisii, is numerously set all 

 round its surface with strong, 

 thorny spines. 



The pinnules mostly vary 

 in shape from the linear forms 

 as narrow and long as pine 

 needles in certain Zamias to 

 the thick and fleshy ovate forms 

 like those of Zamia furfur acea, 

 reminding one of the leafy 

 blades of Dammara and certain 

 of the Cordaitales. In addition, 

 several very peculiarly shaped 

 pinnules occur. Those of 

 Macrozamia heteromera are 

 erass-like blades twice dichoto- 

 c . „, , , , , .. mizing (see fig. 122, G) and the 



rig. 123. — Entire and apinose margins ot pinnules ot existing cycads. X %. ° v ° 



A, Encephalartos (?) lanuginosa ; B, Zamia "glabra"; C and D, much larger pinnules of Ell- 

 Encephalartos Lehmanni (side views) ; E, Zamia (?) vernicosa. cehhalai'/oS Caffer (?) and espe- 



h may be noted that spinose petioles or toothed pinnule margins are rare in fossil . ii . 7^ r 1 .j r/ y,, l/7 ' f r f £rv too 



cycadean foliage, such characters appearing to distinctly increase with the age of Cially ±L. 1.WII 'III till III \CJ. n & . 1-4J' 

 the group, quite in accord with Beecher's theory of spinose growths (2). - , 1 *. qcciiiiie Qr\ UlieQlial 



Y shape, owing to the development of a lower basal spine into a broad lamina, 

 thus forming unequal dichotomy of the blade. In Encephalartos horridus several 

 such laminiform spines are present (cf. fig. 122 c). 



Such variations are also to be considered forms of much modified margin, 

 since other marginal thorns are present. Ordinarily the margins are entire and 

 slightly inrolled dorsally. In Dion the margin is sparsely set with strong thorns, and 

 in Zamia pseudoparasitica it is sparsely serrate. The marginal characters are of only 

 secondary systematic value. In length the pinnules vary- from a few centimeters to 

 half a meter; in texture they are leathery in greatly varying degree; in color they 

 vary from light to a very dark green {Zamia fuscoviridis). 



