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Olive. — Sexual Cell Fusions and Vegctalive 
Material and Methods. 
I am much indebted to Professor J. C. Arthur for the privilege of 
collecting rust material from his laboratory cultures, and for suggestions as 
to the most promising forms for study, as well as for other courtesies. 
I wish to acknowledge my obligations, also, to the Carnegie Institution 
of Washington fora grant which has made possible this collection. Of the 
forty species and more examined, perhaps the most favourable form for the 
study of sexual cell-fusions, as well as of nuclear division, was found to be 
Triphragmium ulmariae (Schum.) Link, on Ulmaria rubra Hill, a caeoma 
form, similar to the Phragmidia studied by Blackman and Christman. 
Cell-fusions are shown most clearly and unmistakably in Triphragmium , 
particularly after the walls of the hyphae have been specially stained ; and 
the nuclear divisions in the spermogonium, as well as in both the gameto- 
phytic and sporophytic cells, show many details not hitherto described. 
Other species in which cell-fusions are described in this paper are : Gymno- 
conia intersiitialis (Schlecht.) Lagerh. ( Caeoma nitens S.) on Rubus sp. ; 
Phragmidium potentillae-canadensis Diet, on Potentilla canadensis ; and the 
micro form, Puccinia transf ormans E. & E. on Tecoma stans Juss. 
Besides the fairly complete series of karyokinetic stages from Tri - 
phraginium , the following species have been utilized for isolated stages : 
Uromyces Scirpi (Cast.) Burr. ( Aecidium Sii-latifolii Wint.) on Cicuta 
bulbifera , Uromyces Lilii Clint, on Lilium canadense and Puccinia Cirsii- 
lanceolati Schroet. on Carduus lanceolaUis L. 
The material for the most part was fixed in various strengths of 
Flemming’s Chromic-acetic-osmic acid mixtures. Some which was fixed 
in Juel’s Zinc chloride-acetic-alcohol mixture proved to be particularly 
favourable for bringing out the cell-fusions, since the cell-walls seemed to 
color with especial tenacity after such fixation. With this method, 
absolutely convincing evidence was obtained as to conjugation pores, and 
as to the extent of absorption between fusing cells. Flemming’s triple stain 
was used almost exclusively. 
Sexual Cell Fusions. 
Figs. 20-40, PI. XXII, inclusive, drawn from four species of Rusts, show 
the method by means of which the binucleated condition suddenly arises, 
following a period of growth which produces only uninucleated cells. All 
four of the species here represented are of the diffuse caeoma type of 
aecidium. Although I have also found cases of fusions in the aecidium-cup 
type, certain peculiarities present in such forms, to be discussed later to 
a limited extent in connexion with nuclear division, necessitate further study 
before these more complicated conditions can be brought in line with the 
simpler caeomas. 
