308 Proceedings of Indiana Academy of Science 



can be attributed to weather conditions. However, it hardly seems pos- 

 sible that fields can be so thoroughly infected with a disease that they 

 "look as if they had been heavily dusted with flour" (Edgerton) and 

 "when the mower goes through the field a white cloud arises on all 

 sides" (Anderson) without the fungus interfering considerably with 

 development and yield of its host. Not only must considerable food be 

 withdrawn from the host by the parasite but also the mat of mycelium 

 on the surface of the leaves and the haustoria within the cells must 

 interfere considerably with photosynthetic activities of the plant and 

 thus prevent, to a more or less extent, the manufacture of the plant's 

 food. The withdrawal of food and the weakening of the plant un- 

 doubtedly brings about the premature death of parts of the plant such 

 as the older, longest-infected leaves but not so rapidly but what new 

 leaves take their place, which in tv;rn gradually are infected. However, 

 the plant as a whole is probably very seldom if ever weakened so 

 much as to succumb entirely except after prolonged attack. In the 

 absence of destruction or serious weakening of all or part of the crop, 

 there is no good basis fcr measuring loss since the widespread occur- 

 rence of the disease precludes the opportunity of comparing diseased 

 and disease-free fields of like fertility, and otherwise compaiable. As 

 indicated above, the enormous mycelial and spore production must reduce 

 to some extent the stored food of the clover plant and correspondingly 

 its feeding value. The premature death of the older leaves and possible 

 increased shattering of the diseased younger leaves is another source of 

 loss. If the second crop of clover is saved for seed, possibly the loss 

 may be more easily measurable since with the lowered food content of 

 the clover plant there is likely to be a reduction in the number or 

 quality of seed matured. 



A matter of considerable concern to the farmers is whether mil- 

 dewed clover is fit for feed. From the evidence furnished by the Plant 

 Disease Survey {I.e. 2) no harm is liable to result from feeding such 

 clover. Hesler reports that tests conducted by the Tennessee Experiment 

 Station indicate that stock (horses, cattle, sheep, swine) is not injured 

 after being fed or grazed 14 days on mildewed clover. Edgerton re- 

 ports that no poison or injurious substance is formed. Dungan quotes 

 C. M. McWilliams, Farm Adviser of Randolph County, Illinois, who 

 observed no ill effects from feeding the mildewed clover to cattle, horses, 

 and mules. There is a possible slight danger in feeding the hay to 

 horses on account of the presence of the spore-dust. Tehon reports 

 a trouble in cartle similar to 'heaves' attributed to mildewed clover in 

 southern Illinois. 



Control of a disease of the nature of mildew under the cultural 

 conditions necessary for clover is extremely difficult, and apparently the 

 only feasible method is in the discovery or development of disease- 

 resistant strains. The biology of the mildew of clover, however, has not 

 been extensively studied. Salmon^ upon a morphological basis, considers 

 the mildew of clovers as Erysiplte Polygoni DC. for which he gives 359 



^ Salmon, Ernst S. A Monograph of the Erysiphaceae. Mem. Torrey Bot. Club. 

 9:1-202. 1900. 



