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FROMME: SEXUAL FUSIONS IN FLAX RUST 125 
perhaps some similarity between them and the multinucleated 
cells that I have found. 
I have examined my material carefully to determine whether 
the binucleated condition is ever brought about by the migra- 
tion of the nucleus of one cell into an adjoining cell, as described 
by Blackman, and have found no such cases in the fertile 
layer of the aecidium, or such as could be considered true fertili- 
zations. Occasionally, however, in the vegetative mycelium 
below the fertile layer of the aecidium, I have found cases that 
are very similar in appearance to some of Blackman’s figures. 
One of these is illustrated in FIG. 28. The nucleus here is evidently 
passing through a very small pore in the walls between two adjoin- 
ing cells and is drawn out in a very fine thread in the passage. 
The two cells are small, contain but very little cytoplasm, and lie 
some distance below the surface of an old sorus which has already 
produced aecidiospores in the regular manner. Another case of 
migrations of nuclei is shown in FIG. 29. Two nuclei from neigh- 
boring vegetative cells are migrating into the same vegetative 
cell. It does not seem possible to connect any of these cases with 
the normal process of fertilization in any way, and the interpre- 
tation of Christman, Olive, and Kurssanow of similar phenomena 
as “pathological” seems most natural. 
UREDO 
The uredosori arise from a binucleated mycelium which results 
only from infections with aecidiospores. They are found on both 
Sides of the leaves and on the stems. The sori are indefinite in 
€xtent, without pseudoperidium or paraphyses except for a few 
Sterile, capitate filaments, which sometimes occur at the outer 
borders of the sorus and less frequently are interspersed among 
the spores within the sorus. The uredospores are borne upon 
long stalks which are made up of two or three elongated cells. 
See FIG. 30, They are large, ovate to elliptical in form, and 
contain two nuclei, as do all of the stalk cells upon which they are 
borne. The walls are thin and finely and evenly verrucose with 
low papillae and equatorial, rather indistinct germ pores. The 
sterile filaments, commonly called paraphyses, which are found 
among the spores, are long and extremely slender and terminate 
