In a section of a piece of lignified coniferous wood recently brought by Col. Feilden from Kolguev island[416], the brown and stout hyphae of a fungus are clearly seen as distinct dark lines traversing the tracheal tissue. The occurrence of septa and the large diameter of the mycelial branches at once suggest a comparison with such recent forms as _Agaricus melleus_, _Polyporus_ and other Basidiomycetes. The age of the Kolguev wood is not known with any certainty. The vesicular swellings such as those represented in fig. 41, A, B, D and E, may easily be misinterpreted. Such spherical expansions in a mycelium, either terminal or intercalary, may be sporangia, oogonia or large resting-spores, or non-fungal cell-contents, and it is usually impossible in the absence of the contents to determine their precise nature. Hartig[417] and others have drawn attention to the occurrence of such bladder-like swellings in the mycelia of recent fungi, which have nothing to do with reproductive purposes; under certain conditions the hyphae of a fungus growing in the cavity of a cell or trachea may form such vesicles, and these, as in fig. 42, D, _m_ may completely fill up the cavity of a large tracheid. Some good examples of bladder-like swellings, such as occur in the mycelium of _Agaricus melleus_ and other recent fungi, have been figured by Conwentz[418] in fossil wood of Tertiary age from Karlsdorf. The swellings in this fossil fungus might easily be mistaken for oogonia or sporangia; especially as they are few in number and spherical in form. A similar appearance is presented by a mass of tyloses in the cavity of an old vessel or tracheid; and vesicular cell-contents, as in the cells of fig. 41, A, 2–5, may closely simulate a number of thin-walled fungal spores or sporangia. A good example of such a vesicular tissue, in addition to that already quoted, is afforded by a specimen of an Eocene fern, _Osmundites Dowkeri_ Carr.[419] described by Carruthers in 1870. The ground-tissue cells contain traces of distinct fungal hyphae (fig. 41, B), and in many of the parenchymatous elements the cavity is completely filled with spherical vesicles; in other cases one finds hyphae in the centre of the cell while vesicles line the wall, as shewn in fig. 41, B. Carruthers refers to these bladders as starch grains, and this may be their true nature; their appearance and abundant occurrence in the parenchyma certainly suggest vesicular cell-contents rather than fungal cells. I could detect no proof of any connection between the hyphae and bladders, and the absence of the latter in the cavities of the tracheids, fig. 41, C, favoured the view of their being either starch-grains or other vacuolated contents similar to that in the cells of the Portland Cycad (fig. 41, A) referred to on p. 88. [Sidenote: PATHOLOGY OF FOSSIL TISSUES.]