Sexual Organs of Phytophthora ery thro septic a, Pethyb . 119 
onwards open one of them every twelve hours and fix the part of the medium 
immediately about the inoculating material. Fixing was done as a rule 
about midday and midnight, that is, in the latter period of the work. 
Great difficulty was at first experienced in finding the earliest stages in the 
penetration of the antheridium by the oogonial incept and the stages of 
fertilization. It was surmised that both possibly occurred at night: Pethy- 
bridge ( 27 ) had watched penetration taking place at that time. It was with 
this in view that the hours for fixing were chosen, and while a greater 
general activity is found in the material fixed at midnight, the earlier 
inability to find the missing stages is to be attributed rather to a lack of 
a sufficient number of sexual organs than to anything else. 
Two lots of material were always fixed at the same time—one in 
Merkel’s fluid and one in chrom-acetic acid. Fixation was allowed to con¬ 
tinue for twenty-four hours, after which the material was cut into convenient 
sizes for microtoming. The sexual organs are formed in the upper layers 
of the medium and they are not oriented in any one particular direction. 
Consequently sections parallel to the surface or at right angles to it are 
equally good and show both longitudinal and transverse sections of the 
organs. Sections cut in the former way, however, are uneven, the lower part 
of the medium containing no’ fructifications, while they lie so thick in 
sections through the surface layers that it is impossible to follow the series 
of sections through a single oogonium. Some of the best material was 
spoiled in this way. On the other hand, the fruit bodies are never so abun¬ 
dant that the series cannot be followed in sections perpendicular to the 
surface. 
The material was washed after fixing for from twelve to twenty-four 
hours in running water and then transferred to 10 per cent, glycerine in 
an open vessel. Watch-glasses may be used for the purpose if filled to 
the brim, but they are hardly deep enough, particularly if the material 
be large in bulk. The vessels should be kept loosely covered to exclude 
dust. After three or four days at room temperature (or near a radiator 
if preferred) the watch-glasses or other containers were placed on the top 
of a paraffin oven for a few hours, or until the liquid had about the same 
consistency as pure glycerine. The material was then transferred to 
95 per cent, or absolute alcohol direct and allowed to remain there about 
forty-eight hours, the alcohol being changed four times to harden the tissue 
and to wash out all the glycerine. This step should not be hurried, but 
it is possible that time might be saved on the preceding one. Up to this 
stage, provided the proper fixing fluid has been used, one may be certain 
that even the most delicate tissue will come through in perfect condition, 
and the process is, in the experience of the writer, much superior to 
dehydration with grades of alcohol and much less troublesome. If 
distortion and injury occur at all it is usually in the transfer from absolute 
