234 Wisconsin Academy of Sciences, Arts, and Letters. 
the haustorium, killing it, and causing collapse of the mother cell and the 
death and plasmolysis of the hypha back of it for some distance. If this 
reaction is rapid, the haustorium is destroyed while still very small; if 
more sluggish, a full-grown haustorium may be formed and some nourish¬ 
ment for further growth be extracted by the fungus. 
She thus points out that the resistant variety Kanred possesses 
three means of defense against this strain of rust, namely, the 
stomata which exclude most of the fungi, the heavy contact walls 
adjoining the attacked cells which are interpreted as preventing 
the diffusion of toxic substances to uninvaded cells, and ‘‘a true 
immunity.’’ In connection with the last the starvation theory 
discussed by Ward (89) and his students (36, 52, 70) does not 
seem tenable since the fungus hyphae appear to grow well in 
the intercellular spaces as long as the host cell is not penetrated. 
Upon invasion of the latter, there is evidence that the host cell 
undergoes chemical changes due to the invasion by the parasite 
and that, moreover, some substance diffuses into the fungus haustor¬ 
ium resulting in its death. That there is irregularity in the 
balance of forces of interaction between parasite and host is 
shown by the fact that in some cases the one collapses first while 
in other cases, the other dies first. 
Preliminary studies of the reaction of Kanred to another bio¬ 
logic strain of Puccinia graminis tritici to which it is known to be 
less ' resistant, indicate that a higher percentage of appressoria 
enter the stomata. It will be interesting to learn the results of 
further study on the interactions between the host and this second 
strain of the parasite. 
Chemotropism as a Factor in Resistance 
Massee (53) would explain the susceptibility or resistance of a. 
plant by the presence or absence of a positively chemotropic sub¬ 
stance in the host cells. The evidence is not convincing, however. 
Numerous cases have been recorded where fungi penetrated plants 
very resistant to their attack. Gibson (36), for instance, found 
that the germ tubes of a number of rust fungi readily entered a 
wide range of plants other than their respective hosts, but no 
further development of the fungus occurred. Wiltshire (95) 
found that the pear scab fungus (Venturia pirina) would invade 
apple fruit and that the apple scab fungus (Venturia inaequalis) 
would invade the pear, but each parasite was capable of producing 
the disease only upon its respective host. Tisdale (79) showed 
