106 Dr. D. Ellis — A Jurassic Fossil Fungus. 



under discussion are plainly revealed. It cannot be reasonably doubted 

 that the fragment marked a in PI. VII, Fig. 3, is an organic fragment 

 similar to the other obviously organic fragments that are to be seen 

 in the same field. It is unfortunate that in the Frodingham Iron- 

 stone in which these were found no traces of the internal structure 

 of the animal host could be discerned, whilst the details of the 

 structure of the parasite contained in it were so clear. This point, 

 however, is capable of an easy explanation if it be assumed that the 

 threads and vesicles represent a fossil fungus which during its 

 lifetime had the same power of absorbing iron salts that the iron- 

 bacteria possess at the present day. Under these circumstances the 

 membranes of the fungus would be impregnated with ferric oxide 

 during its lifetime, a circumstance which would render these 

 membranes much more resistant to disrupting forces than the 

 soft tissues in which they were embedded. Further, it is 

 possible to conclude with a fair approach to certainty that 

 the iron on the threads was laid down for the greater part 

 during their lifetime. The reason for this conclusion is as follows: 

 A study of the iron-bacteria has brought to light the fact that the 

 deposit of iron on their membranes varies in consistency according to 

 the age of the thread. Young threads have a sharply contoured 

 membrane of a brownish-yellow colour. In older threads the nature 

 of the deposition and of the membrane is quite different. The colour 

 of the iron changes to a deeper brown, the quantity of it is greater, 

 and the membrane, instead of being a continuous sharply outlined 

 structure, is a discontinuous irregular line and wanting in sharp 

 lines of demarcation. All gradations can be observed by a close 

 study of the membranes of Leptothrix ochracea, the best known of the 

 iron-bacteria. It is surely a significant fact that the same gradations 

 can be observed on the membranes of the threads which we are 

 now discussing. The appearance of these gradations is easily 

 explicable if we assume that the tubes are the remains of an iron- 

 absorbing fungus, but on the assumption that all the iron in these 

 rocks, including the iron on these tubes, resulted from a subsequent 

 infiltration of iron-charged water, the explanation is not so easy. It 

 cannot be doubted that the bulk of the iron in these rocks arrived 

 there by subsequent infiltration, but it is at least highly probable 

 that some of it has never been absent from the material from which 

 these rocks were formed. If the iron on these tubes had got there 

 solely by infiltration, it would naturally be expected that all the tubes 

 would have a deposit of a uniform nature ; the tubes, on the other 

 hand, show those changes which come about when iron enters the 

 living cell, and after undergoing changes due to metabolism is thrust 

 out again and deposited on the outer part of the membrane. 



We mny assume that the presence of the iron covering is a sufficient 

 explanation of the preservation of these threads and vesicles. Whilst 

 a search among the organic particles of the Frodingham Ironstone 

 containing the fungus failed to reveal traces of the structure of the 

 host, a measure of success was achieved by searching the similar 

 Jurassic ferruginous limestone at Dunliath in the north-west of 

 Scotland. In PI. VII, Fig. 6, for example, we see an organic 



