PARASITIC ON PELLIA EPIPHYLLA. 113 
many rhizoids (really the rejuvenation shoots deseribed on 
page 116) in hanging drops of water containing many spores, and 
kept them under observation for three weeks, but no single 
instance did I see of a germ-tube piercing the rhizoid wall, t. e. 
of penetration of the rhizoid wall from without. Similar hanging 
drops well showed the power of hyph:e to penetrate the rhizoid 
wall from within, and to grow out from them, but in this case these 
hyphe had been nourished at the expense of the contents of the 
rhizoid. This question of infection by the rhizoids seemed to me 
so important that I gave special attention to it. In very many 
sections I found mycelium at the base cf the rhizoids, but I could 
not follow the hyphze into contiguous cells. I had been so much 
struck with the constancy of the progression of the disease from 
the older and rhizoid-bearing part of the thallus towards the 
apical region free from rhizoids, and I had so often found in 
hanging-drop eultures of small pieces of thallus in water that 
while the spores towards the upper surface had not even swollen, 
those near the rhizoids had germinated and their germ-tubes 
had encircled these rhizoids (pointing to some chemotactic in- 
fluence), that I could not help thinking that, even though I had 
specially noticed the cobweb-like mycelium on the upper surface 
of the thallus (see fig. 2), I should find that infection was by the 
Thizoids, and that the fungus was a saprophyte, which by feeding 
on the dead rhizoid had become educated up to a parasitic phase 
and thus enabled to extend to and to kill living cells. But I can 
ind nothing whatever to support this idea of direct infection by 
Thizoids, 
aec Lo) Banging-drop cultures of small pieces of thallus in 
spores o " found that its cells were brown near germinating- 
the tall er germ-tubes, that they resembled in fact cells of 
ver bon Just at the margin of the diseased area : the walls 
collapsed. ah” protoplasm shrunken, and the primordial utricle 
come > the chloroplastids had lost their colour and had 
characterigts together. I endeavoured to produce this 
point of inre, pearance of the disease and to locate the exact 
glass dishes, ton. I kept pieces of thallus in small, covered 
from the di and directly infected them with spores removed 
Some were » T on the host by freshly-drawn glass needles. 
dt in the M in the laboratory dark room, while others were 
Herence in à oratory, The thallus became diseased, but no 
UNN. ocn time required for infection was recognized, the 
— BOTANY, VOL. XXXIII. I 
