﻿FOLIAGE. 97 



relatively much greater size than the others, is a partial indication that the number 

 of bundles in transverse section of the adult pinnule is here approached. A compar- 

 ison of the near numerical agreement in the bundles of sections 167, 168, and 170 

 from C. ingens type, all of which traverse rachi of varying size, leads to a similar 

 conclusion. Moreover, here, as in some living cycads, the young leaves have 

 largely perfected their conductive systems when ready to emerge from the protected 

 position within the armor or apex of the trunk in which they have taken their 

 long, slow, early stages of growth. Only the petiole remains short, fleshy, and 

 immature ; but in life when once emergent, rapid increase in size and length took 

 place, the adult form soon being reached. 



A Method for Plotting the Pinnule Outline and I 'enation of C. ingens. — As has 

 been previously explained in the description of the fronds of Cycadeoidea ingens, 

 any one of the single ranks of pinnules in any of the transverse sections of pre- 

 foliate fronds may be considered as a single pinnule cut serially as many times as 

 there are pinnules present, the more basally cut member of the series being external 

 and the most apical internal or next the axis of the trunk. The number of bundles 

 present in the successive pinnules of a rank — that is, those borne on one side of the 

 rachis — is therefore of interest as representing the bundles in the lamina of a 

 pinnule from base to tip, and thus affording exact data concerning venation ; 

 whence it follows that from any of these transverse sections of prefoliate fronds, 

 passing through or near the rachis, an almost wholly correct figure of the venation 

 and form of a single pinnule may be plotted from the data in the preceding table by 

 assuming the pinnule length, if not actually determined either from eroded surfaces 

 or from sections.* 



The method for the plotting of an approximately correct figure of the outline 

 of one of these young pinnules from the data above given is a simple one. First 

 lay down a vertical series of parallel lines distant about equal to the distance 

 between the pinnule bundles. Next, in the absence of the exact length of the 

 pinnules as determined from sections, lay down the estimated length on one of the 

 lines of the ruled paper taken as a median line ; then divide this line into as many 

 equal parts as there are pinnules cut in one of the ranks of a transverse section 

 of the folded leaf which passes near or through the rachis. Through each of these 

 divisions of the median line draw lines at right angles, marking off on each the 

 corresponding number of pinnule bundles, beginning with the basal pinnule section. 

 Count off successively on each side of the median line as many lines as half the 

 bundle numbers and mark and unite the points so determined. The line thus 

 obtained will be the approximate pinnule outline. The approximate venation can 

 next be indicated by laying down lines corresponding to the initial bundle number, 

 and dichotomizing at the successive divisions as many times as required to indicate 

 the bundle increase until the broadest part of the pinnule is reached. 



* The venation of the plotted figure will be quite correct, but it is to be noted that the sections not being 

 from the same, but the successive pinnules, there will be every here and there a pinnule section which, 

 though distal in position to the one preceding it, may have a less number of bundles in transverse section. 

 Such gaps occur, for instance, in section 169. Were the sections all actually cut from a single pinnule, in- 

 crease and then decrease in number of bundles cut would of course be wholly uniform from base to tip. 



