212 THALLOPHYTA. [CH. 



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 restiag-spores, or non-fungal cell- 

 contents, and it is usually impossible in the absence of the 

 contents to determine their precise nature. Hartig^ 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^ 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, OsTnundites Bowkeri Carr.' 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 



1 Hartig (78). ^ Conwentz (80) PI. v. fig. 17. 



3 Carruthers (70) PI. xxv. fig. 3. 



