RUST OF ANTIRRHINUM. 



51 



Table 4. — Relative Susceptibility of A)dirrhiniim Varieties to P. Antirrhini. 



Cause of Resistance. 

 Resistance of plants to disease has been explained in two general ways : 

 (1) Resistance may be regarded as being related to certain morphological 

 characteristics. Cobb (1892) considered resistance to fungous disease as 

 bemg due to small stomata, waxy coating, and thick cuticle on the host. 

 Freeman (1911) found that increase in bloom on barley leaves made 

 the plants more resistant to rust. Valleau (1915) studied resistance 

 of plums to brown rot. and considered resistance to be due to the pro- 



