48 BULLETIN C57, U. S. DEPARTMENT OF AGRICULTURE. 
Plant 2 was treated exactly like plant 1 except that the inoculations 
were made on the upper sides of the leaves. No infection resulted. 
Plant 3, on April 10 and 15, was inoculated on one branch on only 
the lower surfaces of the leaves. Another branch was inoculated on 
the upper surfaces only. A third branch was left as a check. Weak 
infection resulted on the first branch. A repetition on xApril 29 with 
fresh seciospores gave better results. 
Plant 4, left untreated, was in another inclosure of the greenhouse. 
It remained healthy, showing that infection had not occurred before 
the plants were brought into the house. 
On May 26 similar inoculations were made by Ewert with uredinio- 
spores on the upper sides and lower sides of leaves. Infection 
resulted in the latter case and also a slight infection of the lower 
surface of one leaf which was inoculated on the upper surface. 
Another similar series of inoculations made by Ewert on June 6 
gave infection only on the leaves inoculated on the lower side. He 
fails to say in all cases that the sori formed only on the lower surface 
of the leaves, but his language implies that this is the case. Attack- 
ing the problem in another way, Ewert (37) sprayed Ribes nigrum, R. 
aureum, and R. rubrum, leaves, part on the lower side only, part on 
the upper side only, and part on both sides, while controls were left 
unsprayed. The details are presented on pages 77 to 79. Because 
some leaves which were sprayed on the upper side developed a few 
sori beneath, he appears to be a little doubtful whether infection 
may occur on the upper surface, but he concludes that it ''apparently 
almost exclusively takes place on the lower surface of the leaf." 
The writer and his associates have made hundreds of inoculations 
on the upper surface of leaves of many species and varieties of Kibes, 
without a single direct infection occurring there. Numerous in- 
stances have been noted in these experiments in which infection ap- 
peared on the lower surfaces of leaves that had been inoculated on 
the upper side. This is believed to be due to spores reaching the 
lower surface in some unknown way. In fact it is very difficult if 
not impossible to guard against this. York and Overholts inoculated 
leaves of Ribes glandulosum on the upper side, both with and without 
ring cells, to prevent the spores reaching the lower surface. Slight 
infection occurred on the lower side in some cases where cells were 
not used. Where the cells were used no infection occurred. These 
tests were made on leaves of different ages on plants of various ages, 
from young seedlings up to fruiting bushes. Tubeuf (173) inoculated 
leaves of Ribes nigrum on the upper side by applying the spores in 
water with a brush. All of the leaves thus inoculated remained 
healthy except a single one which had a uredinium on the lower sur- 
face. He was uncertain whether a spore infected it through the lower 
surface or through a lesion on the upper surface. 
