SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 861 
They form a characteristic reticulum as they grow between the cells of the rhizome 
(figs. 29, 3l). Sometimes an entering hypha can be traced giving rise to this 
reticulum by branching (fig. 31). Felted masses or strands of hyphse or tangled 
knot-like masses are present on the lower surface of some rhizomes among the 
bases of the rhizoids (figs. 30, 33). The entering hyphse.seem to come from this 
external mycelium. 
In relation to the mycelium within the tissues, and sometimes outside the 
rhizome, there are oval dark-walled resting-spores (figs. 29, 34). In the early 
stage the spore has the form of a vesicle with its cavity continuous with that 
of the hypha. The wall of the spore, though it acquires a brown colour, does 
not become markedly thickened, and does not show a double contour. These 
spores or vesicles measure about 100 u. Larger resting-spores of the same type, 
and apparently derived from these, have been met with in the adjacent peaty 
matrix (fig. 35). 
Fungus No. 9* (Figs. 36-38.) 
The general distribution of this fungus, which is of common occurrence in the 
cortex of stems of Asteroxylon, and also enters the resting-spores of Fungus No. 2, 
is well shown in fig. 36. The apparently non-septate hyphae occur abundantly 
in the decaying tissue. The hyphae bear spherical resting-spores with a smooth 
wall that is either thin or becomes slightly thickened. The wall of the resting- 
spore, however, frequently ■ appears definitely thickened and rough, but critical 
examination shows that this appearance is due to the spore having been closely 
invested by a covering of the fine hyphae. These can be traced over the original 
thin wall, and their tubular cavities are apparent where the invested wall is cut 
in section (figs. 37 and 38). The diameter of the hyphae is about 3 u, and of the 
resting-spores about 45 u. 
Fungus No. lO.f (Figs. 39-41.) 
This form of fungus is especially common in relation to Rhynia Gwynne- 
Vaughani. It is found in the decaying stems (Part IV, fig. 13) and also in the 
adjoining matrix, sometimes in a sort of exudation from the hemispherical projec- 
tions. Fig. 39 shows a very characteristic mass of the fungus from the peaty 
matrix derived from a broken-down stem, the remains of the xylem of which is seen 
in the upper part of the figure. This figure and the portions of the same mass more 
highly magnified in figs. 40 and 41 show that the fungus consists of a fine non- 
septate mycelium, the hyphae of which form numerous dilatations that are some- 
times intercalary, but more commonly terminal. These are cut off by septa and 
enlarge into the thin-walled globular resting-spores that occur scattered or more 
commonly in masses. What appears to be the same organism also forms longi- 
* Named Palseomyces vestita, below (p. 869). j Named Palceomyces agglomerata below (p. 870). 
