FROMME: SEXUAL FUSIONS IN FLAX RUST 127 
those in the caeoma type, and Olive’s multinucleated cells may be 
correlated with the more definite form and structure of the cup. 
The double layer of sterile cells in Melampsora Lini may possibly 
be comparable to the pseudoparenchyma of an aecidium cup and 
indicate a transition between the more superficial caeoma and 
the deeper cup type of aecidium. The evidence seems to point 
to the conclusion that the short-cycled micro- and leptoforms are 
the more primitive and that such a form as the flax rust with its 
five spore forms is more highly specialized. Itisinteresting to note 
that the less differentiated caeoma type of aecidium can persist 
in these higher types of rusts. 
As to the relationships of the Uredineae with other fungi or 
algae, the preponderance of evidence at present seems to favor 
the view that the present sexual fusions are a substitute for a 
more primitive type in which the spermatia functioned as male 
cells. The existing sexual processes are certainly of a zygosporic 
character. The conjugation is betwen two entirely similar cells, 
which participate equally in the formation of a double cell from 
which a series of spores are produced. This is of course no proof 
that the primitive form of sexuality was zygosporic. Blackman, 
as previously stated, would derive the Uredineae from the red 
algae. While this connection is as yet doubtful, it is perhaps the 
most plausible view of the origin of the group. 
Although Blackman’s observation of a “partial cell fusion” 
by means of “nuclear migrations” in Phragmidium violaceum has 
never been directly disproved, the indirect evidence shown in the 
equal cell fusions that have been found in all other aecidia of the 
caeoma type, so far investigated, leads to the conclusion that 
this form is somewhat aberrant or that the true fertilization has 
not been observed. The further observations of ‘‘ pathological” 
migrations by other investigators and the existence of very similar 
Migrations between vegetative cells of Melampsora Lini, which 
cannot be regarded as true fertilizations, are striking facts. While 
the area of absorption between two gametes may be small at first 
and later broaden, as Olive has shown, there still remains a con- 
siderable difference between the passage of a nucleus as a fine 
thread through an extremely small pore, which cannot be seen 
before or after the passage, and the passage of a nucleus through 
