IOWA ACADEMY OP SCIENCE 
lationship existing between the mycelium and the cells of the host it was 
found that the mycelium penetrated the epidermis directly and made its way 
through the intercellular spaces. 
As soon as the cause of the disease was determined, efforts were made to 
obtain a pure culture. Somehow, I was not able to grow the organism upon 
nutrient agar during the summer of 1909. In the summer of 1910 by the use 
of .1 of 1 per cent oxalic agar medium, I was able to isolate bacteria, and then 
by transfers in the ordinary way, pure cultures have been easily made. After 
having once succeeded in obtaining a pure culture, the organism was trans- 
ferred at different times to nutrient agar, and upon this medium growth was 
more abundant and its action quicker than when grown upon the acid medium. 
In all cases a black pigment is imparted to the medium. Better success, as 
far as pure cultures, was obtained in inoculating tubes, in which leaves of 
barley were placed with the addition of about 5 cm. of water. The organism 
upon this leaf medium grows very rapidly. 
MYCELIUM AND CONIDIA. 
In noting the growth of Helminthosporium teres, it is convenient to begin 
with the conidia. The germ tubes first come from the basal and apical cells; 
later other germ tubes may arise from the remaining cells under favorable 
conditions. As many as three have been observed at one time growing upon 
nutrient agar. Noack^ has figured conidia with four germ tubes appearing at 
the same time for H. graminium (Yellow Leaf Disease). In most cases, how- 
ever, only two germ tubes will be noticed, one from the apical cell and one 
from the basal cell. 
In a favorable medium, like sterile barley straw, under moist conditions, the 
mycelium develops copiously. The early mycelial threads are septate, branched 
and fascicled. In older threads, the cells are constricted somew^hat in thb 
center. In ten days after the sterilized straw is inoculated, the mycelium is 
distributed over the entire surface. After this period, the white character is 
lost and instead, a dark color is imparted. This is due to the large number of 
conidia present. 
The conidia arise from the tips of the conidiophores, and are so loosely 
attached that a gentle breeze or a small drop of water coming in contact with 
them will cause a separation. New conidia will then be formed. This accounts 
for the difficulty of observing the conidia attached. 
In giving the characters of the spores, the description indicated considerable 
variation with reference to color. It has been found that the age of the 
conidia is a factor that determines this point. The younger conidia will be 
of a decided greenish tinge, and vary from a light to a dark color, while the 
older ones are much darker, olive colored, or a gray black. But cultures grown 
under like conditions are found to be the same. 
SCLEROTIA. 
After the culture tubes containing the conidia or spores of H. teres have 
undergone dessication for a time, there is a clumping together of the mycelial 
threads. On examining these clumps, the sclerotia appear as black masses 
that do not conform to any particular shape. These sclerotia vary in size 
from 250u-600u in length and 150u-350u in width. Sclerotia develop readily 
