Lecture IV 



FOSSIL MYCORRHIZAE 



Limitations of the Fossil Record: — Since 1904, when the first 

 paper on fossil mycorrhizae appeared, enough information has been 

 gathered to outline the fossil record of our subject. Yet this record 

 has grave limitations, imposed not alone by scantiness of the in- 

 vestigations but by the nature of all palaeobotany. We have become 

 so accustomed to thinking in the terms of Historical Geology that 

 ofttimes we forget the "geological time table" was created a century 

 ago, when knowledge was far more deficient than it is today, and that 

 later discoveries have been pieced into the Lyellian system, the re- 

 sultant table being far from convincing. It is of interest to observe 

 that Historical Geology is one of the few sciences, perhaps the only 

 science, that has not undergone major revision in the current cen- 

 tury; and, whereas Newtonian Physics has been supplanted by Ein- 

 steinian Physics and other sciences have been critically reworked, 

 Historical Geology continues unrevised. Indeed, no thought of re- 

 vision seems entertained or desired. When the terms of Historical 

 Geology are used, therefore, it is simply an act of convenience, as 

 the writer pointed out in an earlier paper (Kelley, 1939). It can 

 scarely be conceded that the terms "Carboniferous", etc., have any 

 definite time value, yet they are convenient terms since they are in 

 general acceptance and convey some idea at least of the stratum or 

 strata from which the material is derived. 



Sources of Material: — The most hopeful source of material 

 for fossil mycorrhizae is in the Coal-balls which have been found 

 and described from Europe and America. Harder fossilizations in 

 the midst of the coal, they preserve in often intimate detail the 

 structure of root and contained fungus from an extinct flora. Where 

 the fungus is present in actual tissues of the host and shows struc- 

 ture similar to that of living material, we may feel assured that we are 

 dealing with a mycorrhiza; but, where fungi are found in peat or 

 otherwise, it is not so clear that they are mycorrhizal. 



Fossil Phyconiycetes : — Butler (1939) described "the vesic- 

 ular-arbuscular or Phycomycetoid endophytes which commonly occur 



