together and are shorter. Weeping branches may be 1 m., 1.5 m. long, or more, while on badly attacked trees there may be no true weeping branches, but in their place a number of small twigs, a few to 30 cm. long, bearing leaves at fairly crowded nodes. The twigs become distorted with cankers, and tend to curl upwards.

When the twig is first infected a small black elliptical spot appears upon it, which rapidly spreads (Plate 9, fig. 1). Upon this spot whitish acervuli are produced beneath the epidermis of the host, which they raise and finally rupture, setting free the hyaline two-celled spores. As the infected tissue of the twig dies, it dries, cracks, and is broken off by another layer of spores developing below. In this manner several layers may crack off in succession. The canker spreads along and round the twig, and may join other cankered areas, until a large part is involved (Plate 9, fig. 2). The infected leaves become covered with spots, described on pages 60 and 61 (see Plate 9, fig. 3). On badly diseased twigs the leaves, all of which are often infected to some extent, are usually very much smaller than those on healthy branches, averaging 5.9 cm. in length as compared with 12.5 cm. Instead of hanging pendulous against the twigs, they tend to curl and grow more at right angles to it; this is often due to infection of the petiole, causing it to blacken and shrivel. The midrib may also be infected, when elliptical or elongated black spots appear similar to those on the young twigs and petioles. The stipules are often attacked as the leaves unfold, when they drop off at a very early age, while normally they remain at the base of the leaf long after it is mature. Eventually the leaves become yellowish, and fall prematurely. It was observed in early spring that the young leaves were infected immediately on the opening of the leaf-buds (Plate 9, fig. 4), infection probably being caused by spores from cankers upon the living twigs of the tree, from bud-scales (Plate 9, fig. 5), and from dead leaves which had been diseased the season before and remained on the ground. Examination of these during the winter and early spring showed numerous acervuli still producing a large quantity of spores.

Spots similar to those on the leaves, bearing typical acervuli and spores, were also found on the catkins of the weeping-willow.

Pathological Changes in Salix fragilis.—The same fungus as the above occurs on the crack-willow, but much more rarely, and then with less disastrous effect. Blackened areas may be formed along the young twigs, and cankers are sometimes produced on the older ones; but the main effect is seen on the leaves, which become thickly covered on the upper surface with dark-brown or black circular or irregular spots, which differ from those on the weeping-willow by being smaller and more numerous. On the lower surface of the leaves of the crack-willow faint small reddish-brown irregular spots may sometimes be seen; these at times become confluent. The spots are more numerous on the upper surface of the leaf than on the lower. They produce acervuli and spores similar to those on the weeping-willow.