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E. B. MAINS 
host, the tubes were long (about 800 micr.) and somewhat branched. 
In the other two solutions, the germ-tubes were long and abundantly 
branched. Death took place in all these solutions in about four days. 
• Experiment 44. — Cane sugar 3 percent, cane sugar 3 percent plus 
Knop's nutrient, dextrose 3 percent, dextrose 3 percent plus Knop's 
nutrient, Knop's nutrient, and distilled water were used in this experi- 
ment. Pieces of corn leaf were floated on these solutions and the 
solutions were then autoclaved for 30 minutes at 10 pounds pressure. 
This culture was run at the same time as Experiment 39 and inocula- 
tion with uredospores of the rust was made in the same way. 
Infection took place upon the living leaves upon the carbohydrate 
solutions in Experiment 39 in eight days. No development of the 
rust occurred upon any of the autoclaved leaves. 
IV. DISCUSSION 
The first question of interest concerns itself with the condition of 
the tissues in and around the region invaded by the rust. In the 
development of Puccinia Sorghi, it is noticeable that, although most 
of the cells of the leaf may be invaded by the large haustoria, yet no 
harmful effect is shown by the host until after some period of time. 
The rust sends its mycelium through the intercellular spaces and then 
its haustoria into adjacent cells. The invaded cells retain the char- 
acteristics of cells of uninfected tissues. The first sign of effect upon 
the host is seen in the gradual disappearance of starch from the paren- 
chyma sheaths in the invaded region. Since the parenchyma sheaths 
serve as a storehouse for the assimilated material from the adjacent 
region, and since they are not invaded for some time, it would appear 
that this loss of starch is due, not to a withdrawal of starch from the 
parenchyma sheath by the fungus itself, but to the utilization by the 
fungus of the material formed in the neighboring region before it 
reaches the parenchyma sheaths. That, even at this stage, the rust 
is not attacking the host vigorously is shown by the development of 
more or less starch in the parenchyma sheaths of the invaded region 
depending upon the conditions of photosynthesis at the time of obser- 
vation. That the rust is having some effect is shown however by the 
paler color when the parenchyma sheaths of the infected areas are 
stained with iodine. 
This condition prevails up to the time of spore formation. At this 
time, the rust begins to draw more heavily upon the host in order to 
