16 



PALEOZOIC FOSSIL SPORES 



preserved and misinterpreted. Absence 

 of trilete sutures is diagnostic. 



Wall. — Generally moderately thick, 

 mostly 1/10 to 1/25 of the diameter; 

 wall evenly developed on all surfaces and 

 never membranous, often punctate with 

 pores tapering from very small orifice on 

 the outside; sometimes the punctae are 

 very sparse, in other species they may be 

 so densely packed as to give a radially 

 striate appearance. Poorly defined con- 

 centric bands may be present in the wall, 

 but these are ordinarily not easily visible 

 unless material is sectioned. In optical 

 section (transmitted light) aside from the 

 punctae, walls generally appear homo- 

 geneous. 



Affinity. — The question of the affinity 

 of Tasfimnites, so far as it can be def- 

 initely discussed now, hinges on whether 

 these bodies can be taken to represent 

 plant spores or not. Spores of all plants 

 above the algal stage that are readily 

 preserved as fossils have markings on 

 the spore coats of various but definite 

 significance. All plant spores arise 

 normally as tetrads (groups of four) 

 from a single spore mother cell. All 

 primitive plants (aside from algae) show 

 evidences of their tetradic derivation in 

 the structure of the spore coat. The 

 Tasmanites forms do not show any such 

 structure and, in addition, have funda- 

 mentally a unicentric symmetry which is 

 in strong contrast to plant spores which 

 are always radially or bilaterally sym- 

 metrical. Therefore, it seems conclusive 

 that Tasmanites is not allied with any of 

 the known primitive land plants. It may 

 represent an algal type but if so, no cor- 

 relative vegetative algal remains can yet 

 be recognized. 



The ^ preceding remarks indicate that 

 the writers' observations are by no means 

 in agreement with Thiessen's (1921, 

 1925) on what, it appears, must include 

 the same types of material. Thiessen 

 persists in describing all forms from the 

 black shale as if they had "tetrasporic" 

 marks (in some cases more or less 

 removed by abrasion). He definitely 

 identifies them with Dawson's Sporangites 

 huronensis and with the Tasmanites forms 

 illustrated in 1884 by Johnson and 

 Thomas (cf. Thiessen, 1921, p. 293) but 

 discrepancies make it impossible to en- 

 tirely confirm the statement. For ex- 



ample, the form shown on his plate 10, 

 figure A (1921) is stated in the text to 

 be 0.85 mm. (850 microns) in diameter 

 but the legend says it is magnified 140 X, 

 and measurement of the figure shows the 

 form to be at that rate about 170 microns 

 in diameter. It may be this form is the 

 same as some observed in association with 

 Tasmanites in Illinois, but should not be 

 generically identified with it. The walls 

 are generally quite rugulose-undulant and 

 may show a poorly defined very coarse 

 reticulation net, but the membranous char- 

 acter of the fossil suggests that it orig- 

 inally was smoother and that it has been 

 impressed irregularly by grains of the 

 enclosing sediments. No trilete suture 

 (tetrasporic marking) can be demon- 

 strated on material examined at first 

 hand nor is any structure of this sort 

 discernible in Thiessen's figures. Just as 

 Newton remarked in his description of 

 Tasmanites punctatus, 



in none of the sacs have I been able to see this 

 triradiate marking, although their structures are 

 so clearly shown that these markings could not 

 fail to be seen if they were present. 



It must be recalled that the trilete and 

 monolete (haptotypic) structures of cryp- 

 togamic plants are a very definite spore 

 feature, consisting not merely of a ridge 

 which might be abraded from an other- 

 wise featureless surface, but actually con- 

 sisting of two margins, sometimes thick- 

 ened, and a definite suture line between 

 them which cannot be removed except 

 by abrasion of the whole thickness of the 

 proximal wall of the spore. 



Thiessen also fails to make any men- 

 tion of the punctations which are so 

 characteristic of the thicker walled forms 

 referable to Tasmanites, and which are 

 definitely but rather crudely shown in 

 the illustrations of Johnson and Thomas. 

 Had he appreciated what they were, it is 

 doubtful that he would have been so 

 positive that these fossils were spores 

 of pteridophytes, because certainly no 

 known spores of pteridophytes possess 

 such structures. 



The most recent paper bearing on the 

 subject concerns an examination of Tas- 

 manian oil shale by Singh (1932). He 

 considered that he was examining mate- 

 rial similar to that studied by Newton in 

 1875 which contained Tasmanites punc- 

 tatus. However, from the discrepancy 

 in results it may be that he was dealing 



