224 Barrett — - Development and Sexuality of some 
* 3. Study of Sections. 
A. Methods. 
The material used for sectioning was secured as described under the 
heading ‘ Methods and Material \ The substratum bearing the organisms 
was washed in several changes of water in order to free it as much as 
possible from all contamination, then dropped into small phials of killing 
solution. The latter consisted of weak and strong Flemming’s solution, 
medium and strong chrom-acetic acid, and Gilson’s fluid. After killing and 
fixing, the material was washed either in slow running water or by making 
frequent changes by means of a pipette. Dehydration was secured both 
by carrying the specimens through the grades of alcohol, and by evaporat- 
ing down in 10 per cent, glycerine. After clearing in cedar oil, the material 
was embedded in paraffin. Sections were cut 2-5 jut thick and stained on 
the slide. 
The stains used were Flemming’s triple stain, with the orange G. 
dissolved in the clove oil, Heidenhain’s iron-alum haematoxylin, and Gram’s 
stain followed by eosin in clove oil. For most purposes material fixed 
in medium chrom-acetic acid and followed by the triple stain gave the best 
results. The same stain applied to material fixed with Flemming’s 
solutions served best for the maturation stages of the sporangium, and for 
staining the nuclei of the host. Iron-alum haematoxylin was of little 
service, while Gram’s stain was excellent for bringing out the nuclei during 
fertilization stages. 
Very little histologically and cytologically has been done on the 
members of the family Olpidiaceae, and nothing, so far as I have been able 
to learn, on the genus Olpidiopsis in the sense used in this paper. 
Dangeard (7) studied the histology of two species of the genus Psendol- 
pidinm , then called by him Olpidiopsis Saprolegniae i Cornu, and O. Aphano- 
mycis , Cornu. Inasmuch as the two genera are very closely related, it 
seems proper to give briefly the results of Dangeard’s observations on 
the above species. The material studied by him was stained in toto } which 
prevented the clearest definition of the nuclei, especially in the resting 
spores. 
According to Dangeard, the sporangia of O. Saprolegnia, Cornu, 
present two principal phases in their development. In the young condition 
the protoplasm is very much vacuolated, and is composed superficially of 
broad meshes at whose nodes are located the nuclei. The nuclei are very 
small and appear as simple masses of chromatin. From a uninucleate to 
a multinucleate condition the change is rapid, there being present about 
twenty at the time the sporangium reaches its final size. Later, the 
nuclei which have increased in number space themselves, and show 
