﻿9° 



VEGETATIVE FEATURES. 



pact and elegant manner possible. Also, since in the transverse sections of the 

 fossil fronds the pinnules as cut at successively higher levels increase in width 

 slowly and decrease but slowly, and since the broadest sections of pinnules are 

 usually about two-thirds out along the entire number cut, as counted from the side 

 on which lies the rachis, it is clear that at this stage of growth there is indicated a 

 linear to very slightly spatulate outline, partly recalling some of the large and long 

 spatulate leaves of certain species of Cordaites. The number of pairs of pinnules, 

 as seen in transverse sections of five of the fronds from the crown of C. ingens type, 

 together with measurements of rachis and pinnules, is shown in the table here 

 appended. 



The length of the individual pin- 

 nules is estimated to be about 5 cm. in 

 the case of leaf 1, and those of leaf V 

 were much longer, having reached a 

 length of fully 10 cm., and possibly 

 20 cm., this doubtless being, as already 

 suggested, nearly the adult size. Since 

 it can not be known with entire cer- 

 tainty what was the relative amount 

 a section passes above apex of rachis. f rachial and pinnule increase during 



the subsequent growth and expansion of the fronds, the exact length and form of 

 the mature pinnules can only be surmised. But as the vertical thickness of the 

 largest rachis actually bearing pinnules is 8 mm., about one-third the size of the 

 fronds borne by the mature leaf bases is indicated by this comparative measure- 

 ment ; for the vertical thickness of the leaf bases does not decrease rapidly in all the 

 outer portions of the armor and is nearly the same as in the lowermost portion of 

 the petiole and rachis. Evidently, therefore, frond V was about to enter upon a 

 final stage of growth consisting mainly in petiolar and rachial elongation, while the 

 pinnules may even approach the mature size. 



So far as comparisons with living forms go it may be estimated that the mature 

 fronds of C. ingens type were about 10 feet in length. Regarding the general form 

 we may not be wholly sure as to whether it was truncate like the fronds of Zamia 

 floridana, that is, with several of the apical pinnules shorter than those next below 

 them, or lanceolate like the fronds of Dion and Cerotozamia. But this much is 

 certain : The young silicified fronds here described are distinctly truncate, as may be 

 proven by reference to the longitudinal section given in text-figure 49, 3. This is 

 a careful drawing of section No. 47, which was cut from the same frond as section 

 46 (fig. 49, 2), and above and at a right angle to it, as well as in a radial longitudinal 

 direction to the trunk (see also line 00' in fig. 49, 1, of hypothetical frond). Now, 

 in this longitudinal section, pinnule tips regularly emerge at about the same level, 

 both on the side next to the rachis and in the usual position opposite to it or next 

 to the axis of the trunk. It follows, since pinnule tips are seen to appear on both 

 sides of a longitudinal section at an altitude above the extreme tip of the rachis, that 

 the frond is truncate ; that is to say, the apical pinnules were successively shorter, 

 so that the fourth or even fifth pinnule below the apex of the rachis projected beyond 



