Sexual Organs of Phytophthora erythroseptica , Pethyb. 11 7 
and an immense number of slides prepared to get even a few of the sexual 
organs ; besides which, the medium is no better than some other clear media 
which are more easily prepared, such as potato agar. The main part of the work 
was done with cultures grown on ‘ Quaker ’ oat agar, unfiltered, as used by 
Pethybridge and Murphy, 1. c., p. 580 . On this medium P. erythroseptica 
fruits very abundantly, the whole surface being covered with sexual organs. 
It is difficult to say what advantage there is in using the ‘ Quaker " oat 
rather than the unprepared oat, the same formula being employed in both 
cases, yet there is an advantage (Pethybridge and Murphy, 1. c.), and other 
workers with different Fungi have had the same experience. Careful 
experiments have been made using equivalent quantities of ‘ Quaker ’ 
oat and whole oat, calculating 20 per cent, of the latter to be husk 
and using correspondingly larger amounts; also using the said quantity 
of whole oat but removing the husk, yet the prepared oat medium 
always proved the better. The ‘ Quaker" oat has the further advantage 
over the whole oat as first recommended by Clinton (10), that it is easier 
to handle, being finer, and that it contains no husk, which makes sectioning 
easier. 
Preliminary experiments were made to determine the best fixing agents. 
This was done in the following way: Fine glass capillary tubes were made 
and cut in lengths a little less than the width of a microscope slide. 
A drop of the fluid to be tested was placed on the slide between two of the 
capillary tubes, and to this a portion of mycelium was transferred direct 
from a young culture. A cover-glass was then laid on the capillary tubes 
in such a way that it could not crush the mycelium. The slide was placed 
in a moist chamber to prevent concentration and examined at intervals 
until the full influence of the fixing agent could be seen. A couple of hours 
is ample for this. These observations were made almost entirely on conidia, 
which just then turned up in comparative abundance on a single oat-extract 
agar plate. It is unusual for P. erythroseptica to form conidia on such 
a medium (Pethybridge, 27 and 28), and later on, when more were needed 
for the same purpose (for which they are very suitable), resort had to be 
made to another method to obtain them. If a sterile fly be inoculated and 
placed in sterile water in a Petri dish an ample crop is produced. The 
reagent which gave the best results in these tests was Merkel’s fluid of the 
following concentration: Chromic acid, o-i per cent. ; platinic chloride, o*i 
per cent.; and water. It is interesting to note that Claussen had indepen¬ 
dently arrived at practically the same result in his work. The cytoplasm 
was precipitated in an exceedingly fine condition, but it was found, when 
staining came to be done later, that material fixed in chrom-acetic acid gave 
better nuclear figures with Flemming’s triple stain. In the preliminary 
experiments this fixing agent gave a coarser cytoplasm and often caused 
contraction. The proper concentration, or more probably the proper pro- 
