1 1 94 DISEASES NOT DUE TO PARASITES OR OF UNKNOWN ORIGIN 



The diseased fruits exhibit hollow spots assuming different shapes, 

 round or oblong, angular, with a diameter of i to 8-10 mm. In most in- 

 stances the affection does not go beyond the surface of the fruit, but at 

 times it penetrates to the centre, following the septum. The diseased 

 parts do not colour and remain green and hard even during the ripening phase. 

 When the disease is far advanced , the entire fruit remains discoloured and 

 falls before it is ripe. 



It was thought at first that the disease could be identified with the 

 brown rot of the tomato, caused by Bacilliis Solanacearum E. F. vS., but a 

 closer examination did not disclose the presence of any specific pathogenic 

 germ. Attempts at artificial inoculation with infected tissue were entirely 

 negative. Some growers attribute the characteristic affection of the leaves 

 and fruits to the use of hydrocyanic acid fumigations, with which Aleuro- 

 des is controlled, but test experiments carried out to prove this gave negative 

 results. 



Experiments on sterilised soil seem to suggest the existence of a rela- 

 tion between the origin of the disease and the soil, but considering the ab- 

 sence of any pathogenic germ, it must be assumed that the disease is due 

 to some chemical or physical defect of the soil, the action of which is to all 

 appearance mitigated by sterilisation. 



926 - A New Infectious Mosaic Disease in the Cucumber, in America. — Doolittle 



S. p., ill Phytopa'h(ilng\\ \n\. VI, No. ::, pp. 145-147. Baltimore, Md., 1916. 



Experiments and tests in connection with a new " m.osaic disease " 

 observed in the cucumber, carried out b}' the Author in a field at the Sta- 

 tion of Hamilton (Michigan), during the period 1914-1915. The first sym- 

 ptom of the disease is the appearance of black and yellow dappled .spots 

 between which the still green tis.sue stands out in distinct projections. If 

 the infection develops, signs of growth cease, while on the leaves likewise 

 a mosaic maj^ be seen to appear, with dark green and light green spots. In 

 the course of time, the diseased leaves wither and fall. On the shoots at- 

 tacked, imperfect buds develop with dappled foliage ; the flowers are 

 few and the number of fruits set is still fewer. 



The result of the experiments may be summed up as follows : i) al- 

 though it has not yet been possible to isolate the specific pathogenic agent, 

 as the disease spreads very rapidly it obviously is a very virulent disease 

 of highly infectious character ; 2) if infected matter is inoculated into 

 health}' cucumbers, the characteristic symptoms generally appear within 

 a period of 18 to 20 days, while all the control plants remain healthy ; 

 experiments of this kind, with hypodermic injections of sap extracted from 

 the diseased tissues, were carried out in several places in 1914 and 1915, al- 

 ways followed by a clearlj- positive result ; 3) artificial infections are also 

 obtained by tearing off the leaves of a healthy plant and touching the wound 

 with the broken leaf-stalk of a diseased plant ; 4) The fresh expressed juice of 

 diseased plants as well as that from diseased fruits inoculated into a healthy 

 cucumber plant, also produced the disease ; 5) infected extract retains its 

 virulence even if passed through the Berkefeld filter ; 6) aphids contribute 



