G. R. Wieland — American Fossil Cycads. 429 



The largest pinnules are borne on the central portions of the 

 frond. They are 1*5 centimeters in length and bear from twenty 

 to thirty synangia attached to eight or ten closely set nodes. 

 There is here seen, therefore, in the arrangement, form and pre- - 

 foliation a characteristic fern frond, although in the vascular 

 bundles, the entire system of which is indicated by beautifully 

 preserved xylem, there is an advance in the direction of the 

 cycads, by the way, we venture to think of structures of cycado- 

 filicinian type. The statement previously made that this frond is 

 morphologically Marattiacean is however based more particularly 

 on the histology of the synangia. Their resemblance to those 

 of living Marattiacese is a striking one, and involves facts of 

 far-reaching significance. In size, position, arrangement of 

 the sporangia in two parallel rows extending the full length 

 of the synangium, and in dehiscence, they resemble such spe- 

 cies as Marattia Icevis, or cicutwfolia, there being a tendency 

 to greater breadth, a larger number of sporangia, and a slight 

 variation in contour due to appression in interlocking series. 

 But comparisons may be made quite final since the micro- 

 scopic structure of these silicified synangia is preserved entire, 

 bearing in mind that certain cell layers may have already 

 broken down in life at the particular stages of development 

 approaching maturity which most freely permit study. As a 

 matter of convenience, I shall hence describe more fully than 

 I have previously, the typical sorus, or better synangium, as 

 seen in such representative species as Cycadeoidea inge?is, 

 upon which the first descriptions were based, and C. dacotensis, 

 also briefly mentioned and figured in Part III of these studies. 

 (This Journal, May, 1899, Plate X, figures 17 and 18, with 

 text figures 3-16.) 



The pendent synangia, as stated, are thickly set in nodes, 

 being borne on very short stems. See figures 2 and 3. 



Externally the synangium is covered by a layer of heavy 

 walled palisaded cells a single cell in thickness, thickest near 

 the base of the synangium, and thinning out somewhat as it 

 approaches the apical median line, which is that of dehiscence. 

 Just inside this outer palisaded tissue there is a layer of thin- 

 walled hypodermal cells, also usually a single cell in thickness 

 along the lateral wall of the synangium where the individual 

 cells readily collapse, but growing smaller celled and firmer 

 about the bases of the sporangial loculi, and widening out to 

 form the principal ground tissue of the short stem of the 

 synangium as it becomes confluent with the sporophyll. Next 

 to the parenchyma layer lie the sporangial loculi, delimited 

 by deeply iron-stained bands made up of wholly indistinct 

 cell remnants apparently septal in character, with much col- 

 lapsed pollen adhering. No other tissue than that indicated 



