128 
N. C. AGRICULTURAL EXPERIMENT STATION. 
Mycelium was placed so tliat its tips only might come in con¬ 
tact with a lettuce leaf. In twenty-four hours it had grown to the 
leaf, and had developed holdfasts at each point of contact. Each 
holdfast was surrounded by a translucent spot 1 to 2 mm. in diameter. 
In twenty-four hours more the tissues were translucent to a distance 
of about 2 cm. in each direction from the point of original infection, 
though there was no development of mycelium external to the leaf 
except near the petiole where the nutriment afforded by the tissues 
was apparently exhausted. 
TABLE XIV.—SHOWING DISTANCE OF MYCELIAL GROWTH, ON GLASS. 
Amount of Distance of 
Lettuce Leaf Mycelial Growth 
Remarks 
4 sq. mm_ 
4 mm 
50 sq. mm_ 
7 mm 
100 sq. mm_ 
8 mm 
200 sq. mm_ 
18 mm 
400 sq. mm.. 
23 mm 
900 sq. mm_ 
22 mm 
About equally in all directions. 
Irregularly, one small pin-head-sized sclerotium was formed. 
Irregularly, one small pin-head-sized sclerotium was formed. 
Irregularly, one small pin-head-sized sclerotium was formed. 
Irregularly, one small pin-head-sized sclerotium was formed. 
Numerous attempts were made to infect lettuce leaves with soil taken 
from beneath diseased plants and which was known to contain the 
mycelium, since it was clearly visible to the naked eye. 
Thus, on February 8, 1908, fifty lots of such infected soil were taken 
was aseptic precautions by a sterilized spatula and placed upon 
healthy lettuce leaves in sterile culture dishes and dampened with ster¬ 
ile water. No infection resulted. It seems from these tests that the 
mycelium can not migrate far through soil and retain its infecting 
efficiency without additional organic food. 
Hosts. 
While this species of fungus has been reported upon many hosts 
it is notable that during all of our work of the past four years, involv¬ 
ing the inspection of many infected beds in many localities, only two 
cases of the attack of this fungus in lettuce beds upon any plant other 
than lettuce have come under our observation. One of these cases was 
as follows: 
A garden pea about 30 cm. high of vigorous though somewhat 
forced growth, was bent over into contact with the mycelium of the 
diseased lettuce leaf in the experiment mentioned on page 127. In 
eight days the distal end of the pea, some 12 cm. long, had been killed. 
Mycelium was breaking out through it in numerous wooly patches 
and sclerotia had begun to form. The fungus had also migrated some 
9 cm. toward the root and for about 5 cm. the stem was covered with 
floccose mycelium (Fig 28). The invasion of the pea stem continued 
until the entire plant was killed. 
