186 
Geo. K. Sutherland. 
The scattered habit of the perithecia (Fig. 2, 1) hidden all but 
the ostioles by black coverings, very conspicuous on moist thalli but 
naturally difficult to detect on dried material, renders it an easy 
matter to distinguish this species from any of the other fungi 
occurring on this host. The dark pseudo-clypei stand out very 
clearly against the olive-green of living or formalin-preserved 
specimens. 
Fig. 2. DidymospJusria pelvetiana. 1, thallus of Pelvetici showing the 
distribution of perithecia (a) ; 2, surface view with pseudo-clypeus (c) and 
ostiole (o)\ 3, section showing perithecium (a), pseudo-clypeus (c) ; 4, asci 
(a), paraphyses (bj, and ascospore (c). 
The mycelium, intermingled with that of Mycosphcerella, from 
which it differs in thickness and parasitic habit, causes little damage 
to the tissue at first, doubtless on account of its diffused character. 
In this respect it presents a striking contrast to Stigmatea whose 
localised mycelium effects the destruction of infected regions in a 
very short time. Later, browning occurs accompanied by the 
disintegration of the outer cell layers. How far this is due to the 
action of Didymosphccria alone it is difficult to decide, as the tissue 
of the host showed filaments of Elachista clandestina , present often 
in such abundance as inevitably to cause considerable dislocation 
of nutrition, if not actual damage. Although the parasitic hyphae 
frequently encircle the branches of the latter, no direct connection 
has been noted between the two. This, added to the fact that the 
occurrence of Elachista appears to be general on Pelvetia , as 
