54 
Journal of Agricultural Research 
Vol. XIV, No. I 
a manner similar to that in cage i and was planted with two different lots 
of spinach seed. In cage 4 seven of the original field plants were present. 
Of this number one was apparently healthy while the others were in 
various stages of blight. Care was exercised not to disturb the aphids 
which were feeding on the plants. Four commercial lots of spinach seed 
were planted in this cage, care being taken to include lots planted in each 
of the other cages. No attempt was made to free this cage of aphids or 
other insects by the use of nicotine solution. Twelve days after planting 
it was observed that spinach seedlings in each cage were growing vigor¬ 
ously. Twenty-four days after planting, the young plants in all four 
cages appeared healthy, but aphids were observed on the seedlings 
immediately surrounding the mature plants in cage 4, while none were 
present in the three other cages. Ten days later the seedlings in cages 1, 
2, and 3 all appeared healthy, while numerous seedlings in cage 4 bore 
wrinkled, much mottled leaves characteristic of blight. Four days later 
seedlings in cage 4 were dwarfed and mottled, and the cotyledon leaves 
were yellow and were dying. Many aphids were observed on the seed¬ 
lings in cage 4, but none were seen on any of the seedlings in cages 1,2, 
and 3. Seven days later all but a very few of the plants in cage 4 were 
dwarfed and mottled, while the plants in cages 1, 2, and 3 appeared 
healthy. Nine days later photographs were taken to show the charac¬ 
teristic blighted appearance in cage 4 on that date (PI. 10, B) as compared 
with the healthy plants in cage 2 (PL 11, A). Healthy greenhouse plants 
were inoculated with the tissues of diseased seedlings from cage 4. These 
eventually developed typical symptoms of blight. Similar plants used 
as controls remained healthy. The plants in all four cages continued to 
grow until late in May, when the aphids became so abundant in cage 4 
that practically all of the plants were killed. During the 44-day period 
after planting the seed the plants in cages 1,2, and 3 grew more rapidly 
and became much larger than those in cage 4, showing no symptoms of 
blight. About six weeks after planting, the cloth door of cage 3 was 
found open, probably owing to a severe wind storm the night before. 
About 500 plants were removed from cage 3 at this time in an attempt 
to find aphids or blighted plants. Neither were found; so the remaining 
500 plants or more were left in the cage. The experiments in cages 1 
and 2 continued until the end of the season without the plants in either 
cage showing signs of blight. Some time after the door of cage 3 was 
found open, aphids were observed on the plants within this cage, and 
before the end of the season spinach-blight had developed on some of 
the plants. The results obtained in these four cages substantiate those 
obtained in the greenhouse and indicate that spinach-blight is not carried 
in the soil, but is carried from plant to plant by insects or mechanical 
means. 
