118 FROMME: SEXUAL FUSIONS IN FLAX RUST 
autoecious ancestors. The prevalence of heteroecious forms 
with pleophagous sporophytes and the fewness and evident close 
relationship of the hosts of the aecidial stages in these cases, as well 
as the multiplicity and remote relationship of the hosts of the 
sporophyte, support this conclusion. 
Melampsora Lini is quite abundant on cultivated flax, Linum 
usitatissimum, in the vicinity of Brookings, S. Dak. A con- 
siderable quantity of rusted flax straw was collected in the fall of 
gto and was exposed during the winter in a cloth bag suspended 
from a window. In the spring a small plot was sown to flax and 
the rusted straw scattered over the plot. This was watered 
frequently and numerous infections were obtained, the sori 
appearing when the young plants were about five inches high. 
These sori are quite small and it is difficult to distinguish spermo- 
gonia from aecidia. Small portions of the leaves and stems were 
fixed in Flemming’s medium fixing solution, imbedded, sectioned, 
and stained with Flemming’s triple stain and Bendas’ iron haema- 
toxylin. Sections of the uredo- and teleutosori were kindly fur 
nished me by Dr. Olive from material previously prepared by him. 
Melampsora Lini is an autoecious eu-form, i. e., the complete 
series of spore forms, spermatia, aecidia, uredo, and teleuto, are 
all borne upon the common host, flax. The aecidium is of the 
caeoma type, which has been found most favorable for the study 
of cell fusions, and the teleutospores show the nuclear fusions — 
very clearly. 
SPERMOGONIA 
These are rather inconspicuous in color and occur on both sides 
of the leaves and occasionally on the stems. They are produce 
only by infections with sporidia. They are typically flaskshaped, 
without ostiolar filaments and are placed subepidermally. Som& 
times the spermogonium is merely a diffuse layer of spermatio 
phores without a definite flasklike structure. Several of these 
spermogonia may occur in the same localized area but they ar | 
seldom confluent. Their frequent close association with the 
aecidia will be discussed in connection with the development ; 
the aecidium. The spermatiophores from which the spermatid 
are abstricted arise from large rectangular cells which are arran : 
in a regular series at the base of the spermogonium. The sper 
