DOWNY MILDEWS OF THE RANUNCULACEAE 
There are two downy mildew diseases of the Ranunculaceae in America, 
the Plasmopara mildew of anemones and hepaticas and the Peronospora 
mildew of buttercups. While at present it is chiefly the wild species that 
suffer, these diseases constitute a serious menace to the development 
of garden-varieties from the wild species. 
SYMPTOMS 
The symptoms of the two diseases are very similar. The lesions are 
of two general sorts, localized and generalized or systemic, that is, involv- 
ing the entire plant or shoot. It is chiefly the leaves that exhibit the 
effects of the disease. 
Local lesions. Examine the affected leaves of the different hosts 
provided. OBSERVE :— 
1. The pale-gray or brownish color of the upper surface of the 
affected parts, in striking contrast to the green unaffected areas, especially 
noticeable in the anemones; the angular shape of the lesions; to what due? 
Note that nearly the entire blade may be involved. SKETCH. 
2. The white felty coating covering the lesions on the under 
surface of the anemone leaves; violet-gray on the buttercup leaves. 
This felt is composed of the conidiophores and conidia of the pathogene, 
and constitutes the most distinctive sign of these downy mildew diseases. 
(Compare with grape mildew, illustration specimens.) SKETCH to show 
the appearance of the lower surface of the lesion. 
Systemic lesions. The hypoplastic or dwarfing effect of these diseases 
is especially well observed in the individuals which harbor the living 
pathogene in the rootstocks during the winter. The entire leaves from 
such rootstocks, at least the earlier leaves, are affected. In the specimens 
provided, OBSERVE :— 
3. A marked dwarfing of diseased as compared with healthy 
leaves, especially striking in the buttercups. 
4. The more greyish color of affected leaves. This is very strik- 
ing in affected plants of Ranunculus acris L. in early spring. 
5. The continuous coating of conidiophores on the lower surface. 
The affected leaves or portions of leaves soon die and turn black, shrivel 
and become brittle. 
Make sKEeTCHES of diseased and healthy leaves to show contrast in 
size. 
ETIOLOGY 
The disease in anemones and hepaticas is caused by Plasmopara pyg- 
maea (Unger) Schroeter. while Peronospora Ficariae Tulasne attacks 
various species of Ranunculus. They are closely related phycomycetous 
fungi. 
Ti e-history. The activities of these two pathogenes throughout their 
life-cycles are essentially alike. They develop the same kind of organs 
and structures which are, however, distinctive for each parasite. 
Primary Cycle. These pathogenes are obligate parasites, the period 
of saprogenesis being probably one of rest and of development at the ex- 
pense of stored food. 
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