46 
IOWA ACADEMY OF SCIENCE 
mycelium which grows in the intercellular spaces only, and is nourished with 
or without haustoria; (c) with a mycelium which penetrates into the host- 
cells and becomes an intracellular mycelium; (d) lower fungi which live com- 
pletely in host-cells.” 
HOW FUNGI AEE SPEEAD. 
The mycoplasma theory of infection with the seed in view of recent re- 
searches is untenable. 
Dr. H. Klehahn^^ in discussion of the mycoplasma theory of Eriksson, cannot 
agree with Eriksson in regard to this kind of infection. The Puccinia gluma- 
rum did not appear when the sources of infection were absent. Puccinia sim- 
plex and R. graminis made their appearance only when the plants were placed 
in the open air. Seeds coming from plants that had been badly rusted the 
year before produced very little rust when sown. Infection according to this 
author is due largely to spores carried by animals and wind. It also appears 
that plants badly rusted in the fall and permitted to remain in the field produce 
very little rust in the succeeding summer. 
Agencies of Infection. The wind, dew, and rains, insects, snails, and other 
animals, as well as human agencies, are responsible for the spread of fungus 
diseases. 
The Wind an Agent. That the wind sometimes plays an important part in 
the spread of fungus diseases has been repeatedly observed. 
An interesting case is noted by Dr. Halsted^®. The particular field in ques- 
tion had been cut off earlier in the season so that a new growth made its 
appearance, and on September 6th the asparagus brush was about four or five 
feet high, but the rust was only on one side of each plant. The rusted side 
was at right angles to lines drawn from an old and very badly rusted patch 
of asparagus about forty rods away and the source of infection was undoubt- 
edly the old bed. 
Dr. Sturgis^^ calls attention to the infection of lima bean mildew" by the 
wind. Thus he observed the disease abundant on a farm for a distance of 
about one mile on a straight line from the Station but none were observed at 
this time, August 14th, on the Station vines. On the following day two mil- 
dewed pods were brought from the infected farm and the mildew rubbed upon 
the pod of a single healthy plant at the end of each row. The wind varied 
from northwest to northeast and within a week the mildew appeared abundantly 
from the two infected pods and from this plant swept on to the adjacent plants. 
Water as an Agent. Water sometimes helps to scatter fungi as in case of 
zoospores of the potato rot fungus which are motile. Moist leaves coming in 
contact with each other through the wind, must be a factor of some importance 
in the dissemination of such diseases as the Downy Mildews, where zoospores 
are formed. These diseases are always more important during warm years 
when rains are frequent and the atmosphere is humid. 
Fungi Spread hy Insects. We have seen many leaves of grapes affected by 
powdery mildews which showed the outlines of the movements of snails over 
the leaf, the disease appearing^® where the slimy body of the insect came in 
contact with the leaf. Who has not seen numerous flies feeding on the 
25Zeit. Pflanzenk. 1898 : 321. 19 0 0 : 70. 
26Torr. Bot. Club. 25:159. 
Gaz. 25:193. 
