4 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



Cause not determined — Continued. 



Magnolia (31), troublesome if the pulp is not washed off the seed before 

 planting. 



Eucalyptus spp. (8S, p. 45; 131), serious under moist conditions. 



Betula spp. Communication by Dr. Perley Spaulding, of the Bureau of 

 Plant Industry ; found especially susceptible in a Pennsylvania nursery. 



Carob, at United States Plant Introduction Garden, Chico, Calif. Dr. 

 Mel T. Cook states that damping-off is more serious in carob seedlings 

 if the seed is removed from the pod than if pods and seeds are sown 

 together. 



Robinia pseudacacia (13). 



Apple, in greenhouse at the Michigan Agricultural College. 

 Sclerotinia sp. (Europe) : 



Betula (79), a disease of seed and germinating seedlings. 

 Phytophthora fagi (Europe) : 



Fagus. Hartig (59) and many other writers; seriously affected, even 

 in forest. 



Platanus (15). 



Acer (15), A. platanoides and A. pseudoplatauus (86, 104). 



Robinia (59, 73). 



Fraxinus (73). 



Acacia (59). 

 Cercospora acerina (Europe) : 



Acer platanoides and A. pseudoplatanus (58). 

 Pythium debaryanum: 



Tilia europea and T. ulmifolia (137), serious. 



Robinia (75, p. 13-14), killing germinating seed. 



Catalpa (126). 

 Rhizoctonia : 



Citrus seed beds (130) ; much loss. 



Catalpa (126). 

 Botrytis cinerea: 



Catalpa (126). 

 Fusarium sp. : 



Citrus seed beds (130) ; much loss. 



The sugar beet is apparently the only plant whose damping-off 

 diseases have been investigated with any degree of completeness 

 by modern methods. While there is a great mass of literature on 

 damping-off, it is mainly descriptive and on control measures. Most 

 of the reports of the causal relation between the different fungi and 

 the disease in the various host plants have been based on demon- 

 strations of the presence of the fungus in diseased seedlings. In 

 a great number of these cases identification has been doubtful. 

 Even when a fungus is known to belong to a parasitic species, it 

 is by no means certain that the mycelium found belongs to a para- 

 sitic strain. It has been found, for example, that only part of 

 the strains of Corticium vagum occurring in sugar beets are able 

 to attack that host vigorously (38, p. 154). Similar data for pine 

 appear in figures 1 and 2. Furthermore, even parasitic strains of 

 several of the damping-off organisms are so widely distributed as 



