709 



The gummosis becomes fatal for the tree when the gum centres make 

 up a greater part of tlie trunk circumference. According to Fliihler^ lemons 

 suffer most and sour oranges least. Cuttings seem to retain the germs of 

 the disease, and in the same way, grafted specimens seem to give a higher 

 percentage of disease than seedlings which have remained ungrafted. Rich 

 fertilization, heavy watering, clayey soils, increase the evil, which is said to 

 increase also if cover crops, like pumpkins, beans, tomatoes, etc., are grown, 

 which require heavy fertilization. 



Judging by the material to which I have had access thus far, I consider 

 the disease of Citrus fruits to^ be exactly the same phenomenon as the exu- 

 dation of gum in the Amgydalaceae. I consider the excessive addition of 

 fertilizers rich in nitrogen, to be one of the momentarily most frequent 

 causes, which play a brief role also in Germany for the pitted fruits in 

 nurseries. 



i\.mong the Italian authors, Peglion- shares the theory explained here. 

 He calls attention to the fact that the cultivation of cover plants needing 

 rich fertilization is injurious. Stable manure is not very suitable for Citrus. 

 The fruit, to be sure, becomes large but remains thick-skinned and sour. 



Blackleg of the Edible Chestnut. 



According to Gibelli'^ this disease is characterized by the appearance of 

 wilted yellow leaves and small fruit, poor in sugar. In young trees the base 

 of the trunk dries up, the bark turns brown, and its tissues contain concre- 

 tions of tannin as large as the head of a pin. Analyses show all the charac- 

 teristics of plants growing poorly, i. e. a large ash content in proportion to the 

 dry substance. In the ash is found a scarcity of potassium and phosphoric 

 acid and a considerable increase of ferric oxid. 



Because of the ball-like concretions, giving the tannin reaction, the 

 disease seems to me to be related to the disease "Mai Nero" of the grape- 

 vine (see page 219). Comes* describes this form as gummosis. According 

 to Cugini^ this disease, because of which bud development is entirely 

 retarded in the spring, or destroyed, is characterized by the appearance of 

 black stripes and spots on the branches, petioles and ribs, tendrils, and stems 

 of the clusters. The spots extend into the organs and, in fact, the trunk 

 even to the heartwood. Besides this, the disease is characterized by the 

 subsequent appearance of yellowish brown granules in the parenchymatous 



1 Fliihler. Die Krankheit der Agrumcn in Sicilien. Biedcrmann's Centraltalatt 

 1S74, p. 368. 



2 Peglion, V. La concimazione e le malattie nella coltura degli agrumi. Boll, 

 di Entomol. agrar., etc. 1901, in Bot. Jaliresber. 1901. T, p. 479. 



3 Gibelli, La Malattia del Castagno; cit. Bot. Jahre.sber. 1879, II, p. 37.';. Gibclli 

 ed G. Antonielli, Sopra una nuova malattia dei Castagni, ibid. Cugini, Sopra una 

 malattia che devasta i castagneti italiani, ibid. 



4 Comes, II Mai nero della vite. Portici 1882. Primi risultati degli esperimenti 

 t'jitti per la cura della Gommosi o Mai nero della vite. Portici 1882. Sul pi-eteso 

 tannine scoperto nelle viti affette da Mai nero. Bot. Jahresber. 1882. 



5 Cugini, Ricerche sul Mai nero della Vite. Bot. Centralbl. 1881, Vol. VIII, p. 

 147. Nuova indagini sul Mai nero della Vite. Bologna 1882. II Mai nero della Vite. 

 Firenze 1883. 



