872 DR R. KIDSTON AND PROF. W. H. LAND ON OLD RED SANDSTONE PLANTS 
known to develop vesicular dilatations, and thin or thick-walled gemmse or resting- 
spores, though rarely in the profusion shown by these extinct fungi. 
A specially instructive comparison may be made with the fungus distinguished 
by C. West as Stigeosporium* which occurs in the living roots of a number of 
Marattiacese. The non-septate hyphse of varying degrees of thickness, the formation 
of vesicles and their transformation into thick-walled resting-spores, the differentia- 
tion of the wall of which shows an approach to a double contour, are points of 
resemblance. West infers, although only vegetative mycelium and chlamydospores 
were available, a position in the Oomycetes, and compares the resting-spores of 
Stigeosporium with those described for some species of Phytophthora. 
Terminal or intercalary vesicles and thick-walled resting-spores borne on non- 
septate hyphse are also met with in a number of other, fungi which are only known 
as endotrophic mycorrhiza.f The further fate of such vesicles or chlamydospores is 
unknown, even in the case of these existing forms, while in them also other repro- 
ductive organs are wanting. It is, therefore, unnecessary to enter into detailed 
comparisons, and a general reference to such mycorrhizal fungi will be sufficient. 
The comparisons last made naturally lead to the consideration of the question 
whether there is any evidence of an association between the fungi and the Vascular 
Cryptogams in the Rhynie peat suggesting mutualistic symbiosis or mycorrhiza. 
This possibility cannot be dismissed, although it is difficult to obtain evidence that is 
not open to other interpretations in dealing with the more or less decayed plant- 
remains in the deposit. 
It appears to be beyond doubt that many of the fungi were living as saprophytes 
and are associated with the decay of the tissues in which they are found. This is 
clearly the case with the strands of hyphse replacing the phloem of Asteroxylon and 
with such fungi as Palseomyces Gordoni that occur in various parts of the different 
vascular plants. It also holds for others like Palseomyces agglomerata, Palseomyces 
vestita, and most of those to which names have not been given, although they may 
not be so generally distributed. There remains the possibility, however, that some 
of the plants contained a mycorrhizal fungus when they were alive, and further that 
some of the fungi that were evidently living as saprophytes in the peat might have 
come from mycorrhizal fungi taking on a saprophytic mode of life after the death of 
the plant-tissues. 
Certain fungal types are regularly found in association with particular vascular 
plants. Thus Palseomyces Hornese is found in a number of specimens of the rhizomes 
and the basal region of the stems of Hornea. The hyphse are intercellular, and 
their connection with fungus outside the rhizome has been followed. The fact that 
other well-preserved rhizomes of Hornea are without any trace of this fungus is, 
* Ann. Bot., vol. xxxi (1917), p. 77. 
t For numerous figures cf. Janse, Ann. Jard. Bot. Buitenzorg, xiv (1897), p. 53, and various descriptions of 
mycorrhizal fungi, especially those occurring in Lycopodiaceae and Ophioglossacese. 
