858 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
in the development of the latter. The description will be based on such a typical 
growth of the fungus, in which practically everything that a wide comparison of 
other specimens has . shown can be seen. * 
The longitudinally running hyphse in the specimen represented in figs. 6 and 7 
occurred in the inner cortex of a stem of Astevoxylon , the cellular structure of which 
had practically disappeared. Though not as perfectly preserved as is often the case, 
the hyphse can be clearly traced. They range in diameter from about 6 u (fig. 8) 
to 16 or 24 u (fig. 9). A fine hypha sometimes widens out into one of the stouter 
brown-walled hyphse (fig. 9). The hyphse, here and in other cases where they 
have been seen both in the cortex and occupying the place of the phloem (cf. fig. 5) 
appear non-septate. 
In fig. 7 some of the hyphse widen out into oval or pear-shaped thin-walled 
vesicles, collapsed specimens of which also occur. All stages intermediate between 
these and the mature thick-walled resting-spores are found. The oval or spherical 
resting-spores are of large size (about 240 m in major diameter, but with considerable 
variation *), and usually show the double contour of the wall that is evident in 
figs. 6 and 7, and to which reference, has already been made. In favourable cases 
they can be seen to be borne on a hyphal stalk, often, as in fig. 9, arising as a lateral 
branch from a longitudinally running hypha. 
The double contour when best marked (fig. 10) is seen to depend on the presence 
of a clear space separating an outer boundary layer of a brown colour from an inner 
more or less thick layer. Within this, again, there may be remains of the contracted 
and more or less indistinct contents. Sometimes an intermediate layer of the wall 
can be distinguished in place of the clear space ; in other specimens this intermediate 
region is occupied by a brownish material ; in yet other specimens the inner layer 
appears to be connected with the outer layer by fine brown strands crossing the 
space (fig. ll). Comparison of numerous specimens supports the impression given 
by these facts that we have to do with the distinction of layers in an original wall 
and the contraction of an inner layer. 
The resemblance which the spores with double contour at first sight present 
to an oogonium containing a single oospore is thus a superficial one. Nothing 
to establish or justify such an interpretation has been found, though carefully 
looked for. 
Nothing could be ascertained with certainty regarding the contracted contents 
sometimes present within the inner wall, and seen in the figures. The occurrence 
of smaller intrusive fungi within these resting-spores will be dealt with separately 
below (p. 864). 
Fungus No. 3.t (Pigs. 12-14.) 
It is necessary to distinguish as a separate form-type of fungus certain thick- 
walled spherical resting-spores borne on stout hyphse and resembling in construction 
* Thus the specimens in fig. 5 are over 350 /x. + Named Palazomyces Gordoni var. major below (p. 868). 
