82 BOTANICAL GAZETTE [AUGUST 
in Vaucheria are along very different lines, namely those of nuclear 
degeneration, which are in sympathy in all essentials with the events 
now known for gametogenesis in Saprolegnia (DAvIs ’o3), several 
members of the Peronosporales, and certain Ascomycetes. 
These facts give a high degree of interest to Vaucheria, which 
becomes the greater in view of the position which this form takes 
in the phylogenetic systems of many authors as representing a pos- 
sible point of origin of the Phycomycetes. This subject will be 
considered, with its bearings upon the writer’s theory of the origin 
and evolution of the coenogamete, at the end of the paper, under the 
head of “Theoretical Considerations.” 
The material, identified as Vaucheria geminala racemosa, Was 
collected at Chicago, the younger oogonia being abundant late in 
March and older stages a week or so later. Of the killing fluids 
employed, chromacetic acid after the formula of FLemMrnc proved to 
be much the most satisfactory (1 per cent. chromic acid 25°, 1 per cent. 
acetic acid 10°, and water 65°). This formula is } per cent. chromic 
acid and +! per-cent. acetic acid. Chromic acid in excess of 4 per 
cent. produced serious shrinkage. The weaker solution of iridium 
chlorid and acetic acid (Eisen) also gave fair results (} per cent. 
iridium chlorid and 1 per cent. acetic acid). The cytoplasmic structure 
and plastids were perhaps better preserved in the latter fluid, but 
the nuclei did not stain so readily. All mixtures with osmic acid 
baoiead objectionable, because the protoplasm of Vaucheria is filled 
with oils and fats which became so seriously blackened that they 
could not be thoroughly bleached. Chromic acid takes out much 
of these troublesome substances, or at least leaves the material s0 
that it can be readily cleared. Paraffin sections were cut 5 thick 
and stained with safranin and gentian violet. The nuclei are 50 
cpsanes as to require the best of lenses, and the Zeiss apochromatic 
objective 1.5" with the compensating oculars was used entirely: 
The oogonia are somewhat variable in number (2-6) and are 
oS . ce whorl near the end of short lateral branches just below 
cas a antheridium. They commence their development as 
Gf al’ Protuberances which from the beginning are multinucleate 
te ni : eal ein proceeds the process enlarges and takes a glob- 
end of a short sfalk (figs. 2-4). It is evident that 
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