. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. June, 1922 SCIENTIFIC AGRICULTURE 327 Doidge more recently in South Africa. Mc- Alpine named it "Black dot disease"^ an excellent descriptive name. In the late summer and autumn of 1921 I discovered what appears to be the same disease at Macdonald College in Quebec. This is the first time its appearance is noted on this continent and a full description will be given later elsewhere. Symptoms The first symptom is a slight yellowing of the foliage which begins at the tips of leaflets and graduall
. Canadian journal of agricultural science. Agricultural Institute of Canada; Agriculture. June, 1922 SCIENTIFIC AGRICULTURE 327 Doidge more recently in South Africa. Mc- Alpine named it "Black dot disease"^ an excellent descriptive name. In the late summer and autumn of 1921 I discovered what appears to be the same disease at Macdonald College in Quebec. This is the first time its appearance is noted on this continent and a full description will be given later elsewhere. Symptoms The first symptom is a slight yellowing of the foliage which begins at the tips of leaflets and gradually involves the whole leaves. It may or may not be accompanied by dwarfing of the plant depending upon the earliness and severity of the infection. The yellowing will show early in the season on plants heavily infected but usually it is a midsummer symptom. The yellowing is followed by browning and withering of the leaves and if moist conditions prevail minute black sclerotia will develop on the surface. At this time the lower stem parts are covered with sclerotia and gradually the stem dark- ens and becomes brittle. On opening the stem the pith is seen to be disorganized and sclerotia line the inside walls of the vas- cular cylinder. Figure 13 indicates the size and number of the sclerotia both on the in- side and outside of the stem. Roots and rhizomes are attacked and the tubers are cov- ered with the minute sclerotia. It apparently does not cause serious damage to the tuber since the mycelium is confined to the super- ficial tissues and the sclerotia are developed on the surface or are slightly erumpent. Mycelium is to be found throughout the stem and leaf tissues of yellowed plants which have sclerotia on the leaves. The org^anism Ducomet describes the sclerotia as astomic pycnidia 75—150 microns in diameter with setae 100 to 130 microns long and at least biseptate. The spores are sliglitly curved and 18-22 microns by to 3 microns. In my cultures the spores are slight
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