114 FROMME: SEXUAL FUSIONS IN FLAX RUST 
the ‘‘sterile cells’ above the ‘fertile’? or female cells as trich- 
ogynes. On this view the Uredineae are derived from the red 
algae. Christman considers the ‘‘fusion of equal gametes” as a 
true fertilization in which a ‘‘non-resting zygospore”’ is produced. 
He suggests that the nuclear migrations of Blackman may be 
pathological in nature like similar migrations observed by him in 
the teleutosorus of Puccinia Podophylli. The sterile cells are 
merely ‘‘buffers’’ and the spermatia may be degenerate gameto- 
phytic conidia. Christman has also found a fusion of equal cells 
in the formation of the primary uredospores in Phragmidium Poten- 
tillae-canadensis, thus showing the morphological equivalence be- 
tween the primary uredospores and aecidiospores. 
Olive, in his 1908 paper, described a further series of forms: 
Triphragmium Ulmariae, Gymnoconia interstitialis (Caeoma nitens), 
Phragmidium Potentillae-canadensis and the microform Puccinta 
transformans. He also studied nuclear divisions in three other 
species: Uromyces Scirpi, Uromyces Lalu, and Puccinia Cirsii- 
lanceolati. Triphragmium Ulmariae has a crustlike primary 
uredosorus very similar to that of Phragmidiuwm Potentillae- 
canadensis, studied by Christman. In this form Olive finds 
numerous cases of wide open cell fusions of the type described by 
Christman. The fusion pores, however, may be of varying 
diameters. In most cases they are broad, the intervening cell 
walls being entirely absorbed, but occasionally the pore is narrow 
so that the nucleus is constricted somewhat in passing. He found 
no cases, however, where the nucleus is drawn out in a fine thread 
in passing through an imperceptible pore as figured by Blackman. 
He further observed, that although the fusing cells may be placed 
side by side in the same plane, as Christman found them, one of 
the gametes is perhaps more often found to lie somewhat below 
the other. In such instances only the upper of the fusing cells 
appears to have cut off a sterile cell. When the two gametes 
are not in direct contact a very short conjugation tube may 
apparently be formed (fig. 26). In all cases figured in Tri- 
bhragmium, only one of the fusing cells enlarges and becomes the 
basal cell. This method of forming the basal cell is quite different 
from that described by Christman for Phragmidium Potentillae- 
canadensis, where the fusing cells combine to form the basal cell. 
