PARASITIC ON PELLIA EPIPHYLLA. 107 
appearance,” well shown at 7.30 a.m. on Saturday, June 13th. 
At 6.48 a.m. on Monday, June 15th, two small white patches 
appeared and increased in size during the week, new and similar 
patches appearing day by day and similarly enlarging. By 
6.45 a.m. on Monday, June 22nd, the centre of the patch had 
acquired a distinctly green colour, which darkened until at 
6.50 a.m. on Friday, June 26th, it was quite brown and under- 
went no further change in colour. 
From these two instances spore-formation seems to occupy 
more time in gelatine growths than on the host. This seems to 
be due only to the fact that in the host there is a speedy ex- 
haustion of the material available, whereas in the cultures there 
is a much greater supply: hence, while a single cluster appears 
on the host, successive clusters appear on the gelatine. 
Hangiug-drop cultures proved more instructive than flask- 
and tube-eultures. I proceed thus in making them :—I heat a 
slide in a Bunsen-flame to clean and sterilize it; I then take a 
glass ring and heat it, and allow one edge to just touch the 
surface of some boiling paraffin. I then place the ring on the 
slide, and let the cell thus formed cool. The rings were cut 
from hard glass tubing about 15 mm. outside diameter and 9 mm. 
inside ; both surfaces were ground and well polished ; so that I 
had short lengths of the tubing 4 min. long. I now take some 
well-cleaned, thin, circular cover-slips and heat them between 
strips of mica in the Bunsen-flame, and let them cool. I place a 
drop of sterile nutrient gelatine (p. 109) in the centre of the cover- 
slip, and sow in ita very few spores taken from the top of a spore- 
cluster with fr eshly drawn glass needles. I then invert the cover 
on the cell, in which I have put three or four drops of freshly 
boiled distilled water; and thus I have a few spores in a small 
pinging dr op of some medium, growing in a moist chamber. If 
the rin © ou ture to last for some days, the cover-slip is sealed to 
of the Sia ut vthorwise the polished surface of the ring permits 
dip. If TA y close approximation of the surface of the cover- 
them m my culture-drops evaporating or the growth in 
minute or M to require more moisture, I rest the slide for à 
vaporizes s Wo on the tip of my finger, the heat from which 
densed on que of the distilled water, and this vapour is con- 
moistened M cover-slip, and my culture easily and satisfactorily 
also able i y the kindness of Professor Marshall Ward, I was 
9 use his improved form of cell for hangiug-drop 
