FROMME: SEXUAL FUSIONS IN FLAX RUST 121 
tative condition. It seems quite probable that they arise from 
common points and that branches from the same mycelium may 
form both kinds of sori. The aecidium and spermogonium are 
frequently separated only by the outer sterile layers of the sper- 
mogonium. Their development proceeds simultaneously, sper- 
matia and aecidiospores being formed at the same time and often 
found lying in the same cavity under the epidermis. Sometimes 
the spermatia are already present when the aecidium has just 
reached the stage of sexual fusions. One of the difficulties in / 
assuming that the spermatia are male cells has been the inaccessi- 
bility of the cells of the aecidium to fertilization by them and the 
production of the spermatia prior to the development of the 
aecidium. Here we have a case, however, where the two develop 
at the same time, and so near together that fertilization might 
easily be accomplished. 
The large vertical cells of the aecidium now begin to conjugate 
in pairs. This conjugation is brought about by an absorption of 
the intervening cell walls at the area of contact. The upper 
portions of the cells involved are usually in contact so that the 
absorption takes place in this region. See Fic. 7. The lower 
Portions of the cell walls are usually not absorbed and the fusion 
cells formed remain with a conspicuous two-legged base. At the 
time of fusion the cytoplasm of the gametes is quite dense and 
stains readily, consequently they stand out quite sharply differ- 
entiated from the vegetative cells below, which have lost most of 
their contents. They can readily be distinguished under the low 
Powers of the microscope without the aid of the oil immersion. 
Sometimes the tips of the gametes converge and the point of 
©ontact and absorption is at the center, as in FIG. 8. The area 
absorbed may be of varying diameters, as Olive holds, but the 
Passage of a nucleus through an imperceptible pore has never been 
observed in the case of the true fertilizations. Certain cases of 
nuclear migrations which are apparently of an abnormal nature, 
will be referred to later. The fusing gametes do not always lie 
side by side at the same level in the sorus. They may meet 
at various angles, and frequently one of them lies somewhat 
below the other. See ric. 9. I do not believe, however, that in 
Melampsora Lini this indicates a difference in the time of develop- 
