98 
IOWA ACADEMY OF SCIENCE 
effect is imparted to the vitality of the spore, for transfers made from such a 
culture showed as much growth in a given time as a transfer made from a 
culture that does not possess this character. 
The growth and development of the conidia under different degrees of 
temperature is a point of considerable interest. Cultures kept in the ice box, 
where the temperature was on the average 5 degrees C., showed considerable 
growth at the end of a period of seven days. Cultures at room temperature 
showed good growth at the end of 72 hours. The optimum temperature for 
growth took place between 23-25 degrees C. At this temperature enough conidia 
had developed at the end of 24 hours to impart to the medium the dark pigment, 
characteristic of all cultures of Helminthosporium. The same general con- 
ditions with reference to temperature apply to sterile leaf cultures. 
The amount of moisture plays an important part in the development of the 
conidia. Where sterile leaves were used as a medium without the addition of 
water at optimum temperature conditions growth could not be induced. In 
the tubes where about 5 cc. of water had been added, the growth was luxuriant. 
This point further emphasizes the fact that the amount of moisture plays 
an important role, not only in cultural wor^ but in the field as well. 
INFECTION. 
The carrying over the fungus from one year to another is an important mat- 
ter from a practical point of view. In this respect the conidia are the im- 
portant factors. The infection from the conidia may be placed under two 
heads: (1) the primary conidia; (2) the secondary conidia. The primary 
conidia are responsible for a direct infection of the seed, and the transmission 
to the first leaves. The secondary conidia are derived from the primary 
spores and serve to spread the disease to unaffected parts. These conidia 
developing in turn may, under favorable climatic conditions, destroy the entire 
field. 
The work of H. L. Bolley^' in regard to the soil as an agent in carrying 
certain cereal diseases is important. The “worn out” soils so commonly de- 
scribed as due to a lack of chemical constituents, are due to the presence of 
such fungi as Helminthosporium species. 
Although the complete life history of H. teres is essential in placing the 
fungus in its right place as far as classification, yet all forms are not essential 
for the propagation of the disease in nature. The possible methods of in- 
fection may be summed up as follows: (1) by mycelium located in the glumes; 
(2) by conidia that are upon the seed or in the soil; (3) by sclerotia that are 
in the soil or upon dead leaves or straw; (4) by pycnidiospores that may form 
upon the straw, of barley grown the previous season; (5) by means of 
ascospores. 
REMEDIES. 
a. Resistant Varieties. 
Whether or not certain varieties are more resistant to this particular fungus, 
is a subject that will need further investigation. Prom a general study of the 
college barley plots in the summer of 1909, the variety known as Chevalier was 
particularly susceptible, while Oderbrucher was practically exempt. It also 
appeared as if the early varieties were not attacked to the extent that the later 
