DISEASES OF PLANTS. 865 



Apple scab, G. P. Clinton {Tllinois Sta. Bui. 67, pp. 109-156, j)h. 4, figs. 34). — 

 In a previous l)ulletin of the station (E. S. R., 11, p. 258) an atrount was given of 

 investigations for the prevention of apple scab. The present ))ulletin records the 

 results of botanical studies made during the years 1898 to 1900. The author has 

 demonstrated the relationship between the parasitic form which causes the well- 

 known apple scab and the saprophytic fungus found upon the decaying leaves. As 

 a result of his investigations the author is le<l to believe that the saprophytic form 

 is the one in which the fungus is carried through the winter. The Fusicladium or 

 ])arasitic stage is described at some length, with the results of experiments in the 

 geiiiiination of the spores and experiments with artificial cultures. The Venturia or 

 saprophytic- stage is also described at length. After the scab-infected leaves fall from 

 tlie trees in the autumn they lose their green color and the mycelium contained in 

 them undergoes slow changes. The rounded cells enlarge and gradually assume a 

 reddish olive color and give rise to similarly colored mycelium filaments that pene- 

 trate into the interior of the leaf. In this way the Venturia stage is produced from 

 the mycelium of the scab stage. The Venturia stage was found most abundant in the 

 spring of the year, when the apple scab was the v.orst. In an especially severe win- 

 ter the cold apparently destroyed many of the perithecia, as few of them were found 

 to come to maturity. The perithecia show on the leaves as small black jtustules, 

 generally st-attered about on grayish spots, which mark the place of the fall si'ab col- 

 ony. When mature they are more or less loosely embedded in the leaf tissues, and 

 at the time of their disappearance infected leaves often show numerous small holes 

 where they have been embedded. The microscopical appearance of the fungus and 

 germination of its spores are described and the results of artificial cultures, in which 

 the 2 fornas are connected, are given. In this way the author has established the 

 identitj'^ between the 2 forms, and it is claimed that the name given to the fungus 

 should be derived from the mature form, and this should be Venturia inaqualis. 

 Moreover, should the fungus occurring on the pear prove different from that upon 

 tlie a{)ple, the specific name of the apple-scab fungus would then be T'. pomi. An 

 extended liibliography of apple-scab literature completes the bulletin. 



On the power of some peach trees to resist the disease called yellows, 

 E. W. Morse {Bui. Busseij Inst., 3 {1901), I, pp. 13). — A brief resume is given of the 

 various factors which have been hitherto attributed as causes of the disease known 

 as peach yellows, and an account given which seems to show the varying suscepti- 

 bility of varieties to serious injury from this cause. According to the author a seed- 

 ling variety known as the White Magdalene has been grown for 150 years without 

 showing any tendency towards disease. The author believes that the principal 

 causes of peach yellows will be found in the atmospheric influences rendering plants 

 more susceptible to disease, while the active agent he believes to be enzyms wliicli 

 may be carrie<l from one plant to another by pollen when the plant is fertilized, and 

 which only manifests itself after a number of years' development. 



Silver-leaf in peaches [Card. Cliron., 3. ser., 30 {1901), Nos. 769, p. 220; 770, 

 pp. 247, ;^^<?).— This disease of peaches, nectarines, etc., has been known in England 

 for at least a (luarter of a century. The leaves retain their normal form and are 

 neither spotted nor blistered, but are deprived of a large portion of their chlorophyll, 

 assuming a silvery appearance, and the whole tree becomes sickly and unproductive. 

 No sjmts or pustules of any kind are detected on the leaves, nor lias any fungus l)een 

 found in any of the tis.sues, but at the same time the disease seems to be conmnmi- 

 calile. It is believed that this di.sease is closely allied to that known as the peach 

 yellows in this country, and is possibly a modification of it. In a subseiiuent com- 

 umnication an account is given of this di.sease occurring on uectarine trees. The 

 writer states that the disease appeared on one branch of the tree from which all the 

 affected leaves were removed and a heavy application of licjuid manure, to which half 



