530 Wisconsin Academy of Sciences, Arts, and Letters. 
the capacity or the incapacity for maintaining certain work¬ 
ing relations between the haustorium and the host cell.” Sal¬ 
mon further attempts to explain immunity by supposing that 
“a power is possessed by the host plant of preventing by means 
of certain physiological processes the attainment of that bal¬ 
ance whereby these working relations are brought about and 
maintained.” What he thinks these “physiological processes” 
are, is not stated. I am of the opinion that, for all evidence 
given, they may be chemotactic as well as anything else. It 
may well be that in the cases cited the haustoria of the fungus 
push into the host cells in spite of substances formed by the 
cells to prevent their entrance. Such chemical substances which 
tend to kill the haustoria may not be in sufficient quantity to 
prevent their entrance, but may be, none the less, sufficient to 
prevent their complete development. 
In all cases investigated the ascospores are limited in their 
infection capacity in the same way and to the same extent as 
conidia from the same host. Marchal (16) states that as¬ 
cospores of Erysiphe graminis DC. from rye will infect this 
host but not wheat, oats, barley, or Agropyrum caninum; as¬ 
cospores from wheat will infect only wheat; and ascospores 
from barley will infect barley ( Hordeum vulgare ), H. dis- 
tichum, H. zeocriton and H. trifurcatum. These results have 
been partly verified by Salmon (25), who used ascospores from 
barley. He has further found (32) that ascospores from Bromus 
commutatus will infect this species and B. hordeaceus, but not 
B. racemosus. Voglino (37) states that ascospores of Phyllac- 
tinia corylea taken from Carpinus will not infect Fagus but 
will infect Carpinus and, conversely, ascospores from Fagus 
will not infect Carpinus but will infect Fagus. 
In this connection it is interesting to note that Salmon (34) 
has described three distinct morphological varieties of Phyl - 
lactinia corylea (Pers.) Karst, based upon the characters of 
the conidia and conidiophores. The variety angulata has co¬ 
nidia varying in size between 45 and 55/x lone: and between 22 
and 26 /a wide; they may be rounded, truncate or bluntly apic- 
ulate at one or both ends, and more or less constricted in the 
middle. It occurs on several species of Quercus, Castanea 
