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REPRODUCTIVE STRUCTURES. 



The tissue of the filiciform pinnules is present, but not very clearly indicated, 

 although traces of bundles with few elements are every here and there to be detected, 

 as well as vestiges of the original ground tissues. This, together with the coloring, 

 gives the tissue a very similar appearance to the unstained fertile pinnules of such 

 ferns as Osmunda and Botrychium. 



The synangia. — The alternately attached and short-stemmed polliniferous 

 svnangia are several times broader than long, and do not differ greatly in size from 

 the sporangiferous synangia of various species of the tree fern Marattia. The main 

 difference in outline from the latter is due to the fact that 

 instead of being freely borne as in the ferns, these fossil 

 synangia, being so densely crowded in the unexpanded flower 

 nearly up to the time of maturity, exhibit, together with basal 

 buttressing, varying appression faces and minor angles, and 

 are usually subcrescentic in transverse section. Similarly 

 to Marattia, there are two parallel rows of elongate spore 

 sacs and a further close agreement in general structure, as 

 will appear from the following description of the mature 

 synangia. The outer layer of the synangium is composed 

 of heavy-walled palisaded cells a single cell in thickness, and 

 is thickest just above the syuangial base, where it forms a 

 heavy buttress, but gradually thins out to about half the 

 basal thickness at the apical median line, which is that ol 

 dehiscence. Just inside this outer palisaded husk there is 

 a layer of thin-walled hypodermal cells, 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 sporophylls. Next to this parenchyma layer lie 

 the sporangial loculi in two rows, one on each half of the 

 synangium. The loculi are usually delimited by deeply 

 iron-stained bauds made up of indistinct remnants of septal 

 cells, with much adherent collapsed pollen. No other tissue 

 than that indicated by these bands separates the adjacent sporangial loculi, of 

 which there are from 10 to 20 in each of the two rows. On the inner side of each 

 row of loculi, as so delimited, there is, finally, a well-defined layer of small elon- 

 gate cells a single cell in thickness, or several cells in thickness, between the angles 

 formed by the adjacent sporangia, and thus covering the entire inner face of the 

 synangium, which was early cleft down to the sporangial bases. 



On the inner middle surface of each sporangium the wall tissue weakens to form 

 a well-marked dehiscent line, along which splitting is frequently seen to have taken 

 place in the unexpanded stage of frond growth, though such premature dehiscence 

 may be due to the process of silicification. Recapitulating, the principal features of 



Fig. 82. — Cycadeoidea daco- 

 tensis Macbride. X 40. 



Longitudinal transverse section 

 through a synangium, showing 

 attachment to the sporophyll, the 

 several layers of the synangia! 

 wall, its dehiscence, the attach- 

 ment of sporangia, and inter- 

 vening median sulcus or fissure. 

 The basal buttressing of outer 

 wall is characteristic. 



