PARASITIC ON PELLIA EPIPHYLLA. 111 
conidiophore. There was also a distribution on the host, for 
towards the end of June and onwards the surface of the thallus 
in the pan seemed to have received a copious supply of “ soot 
dew,” but on examination it proved to be only the spores shot 
off from the clusters and now distributed over the thallus. 
In some hanging-drop cultures in which watery extract of the 
Pellia thallus was used as the culture medium, I noticed a 
striking deviation from the growth described above, and which 
growth I feel justified, after many cultures, in considering 
“normal.” This deviation occurred some days after germination. 
Spores were sown in the ordinary manner, and had after some 
days put out germ-tubes. As they were not in nutrient gelatine, 
I hardly expected them to produce a large mycelium, but I 
found that the germ hypba neither branched nor formed septa 
but that its apex swelled, the contained protoplasm became more 
granular, and, in fact, a secondary spore (Pl. 7. fig. 19) was 
produced, like those described by Plowright for uredospores, by 
Marsball Ward for Pythium and Phytophthora infestans, and by 
no means uncommon. I found, too, that these secondary spores 
might be interstitial as well as terminal (fig. 20): thus in a 
cover-slip culture of spores in watery extract, I found both 
terminal and interstitial secondary spores, the latter closely 
resembling those so copiously formed in the mycelium of Mucor 
when grown for some days on nutrient gelatine. This secondary 
spore-formation went on also in the gelatine hanging-drop 
cultures, but only after several weeks, and after the formation 
of many conidia (see figs. 21-25). The formation appears to me 
to be associated with deficiency of nutriment, either by its 
absence from the medium or caused by the exhaustion of the 
supply by conidia-formation. 
A very interesting point to be learned from cover-slip hanging- 
sap cultures is the fact that, in some cases at least, the spores 
that 10t germinate in the absence of a sufficient food-supply, and 
at In other cases the starved hyphz are roused into vigorous 
Mar oar? feeding. Cultures in watery extract were started on 
only a and by June 11th some showed that the spores had 
covers " and at most a very small proportion on any 
germinated. germinated ; in some cases a single spore ouly had 
Pellis ü " Some of these cultures were fed with a section of 
allus, the remaining cultures acting as controls. In one 
case th P 5 "D 
e swollen spores put out hyphæ, 50 to 100 divisions 
