1906] OLIVE—NUCLEAR AND CELL DIVISION OF EMPUSA 255 
travel forward, so to speak, and to seek a favorable environment in 
which to grow. BREFELD (’83) seems to think, in the case of the 
similar phenomenon in Ustilago, that the cells which are thus cut off 
behind are empty, and that in this way no protoplasm at all is wasted 
in the process. If this were true, a cell-wall would be formed from a 
single plasma-membrane, thus differing from the division described 
above, in which the membrane is split so that the wall is deposited 
between the two. But the apparently empty cell retains its turges- 
cence for a time before collapsing, thus proving that there is at 
least a film of protoplasm present. Further, sections of similar con- 
ditions in which conidia are cut off from a basal shooting-cell (jigs. 
28, 36, 38), show clearly the thin primordial sheath of enucleate 
protoplasm in the lower cell. The fact that the protoplasm of these 
lower cells seems to undergo speedy degeneration contributes another 
point in favor of the idea of the vital importance of the nucleus 
in nutrition. 
I am at a loss to understand why the conidium should be regarded 
by THaxTER (’88, p. 143) as a one-spored sporangium, since in all 
the sections of conidia which I have examined there is no sign of a 
second inner wall. It may be that the plasma-membrane of the plas- 
molyzed contents of a conidium may have been mistaken for a wall; 
or, again, it is possible that this author’s figs. 320, 321 represent con- 
idia still surrounded by the slimy protoplasm which is sometimes dis- 
charged from the ruptured basal cell. 
I wish in conclusion to express my hearty thanks to Professor R. 
A. Harper for the privileges afforded in his laboratories; to Professor 
W. S. Marsua tt, for assistance in the determination of insects; and 
to the Carnegie Institution of Washington, for a research assistancy 
under which this work has been done. 
SUMMARY. 
1. Life history.—The life history of Empusa sciarae may be 
summarized as follows: The disease attacks both larvae and adults 
of the host, Sciara, causing ultimately their death. The young, 
uninucleate germ-tubes, after they have entered the body-cavity of 
the insect, grow there at the expense of the nutrient fluids. After the 
protoplasm has increased in amount, a branching, coenocytic myce- 
