DISEASES OF PLANTS. 447 



practically impossible. The use of a 3 : 3 : 50 Bordeaux mixture lias proved 

 beneficial both in laboratory tests and when sprayed upon plants. Lime 

 sulphur, which has been tested as a possible substitute for Bordeaux mixture, 

 appeared to be injurious when applied at a strength sufficient to kill the spores 

 of the fungus. 



Leaf -roll disease of potatoes, IV, O. Reitmair {Ztschr. Landw. Versuchsw. 

 Ostcrr., 15 {1912), No. 1, pp. 1-106).— This is the fourth report by the committee 

 on the study of this disease (E. S. R., 27, p. 351), the principal conclusions in 

 which are as follows: 



The primary potato leaf-roll disease entails on the plants alterations which 

 affect both plant and tuber, and tend toward a rapid deterioration of the stock. 

 This deterioration through successive generations is accelerated by unfavorable 

 life conditions, but it may be checked or for a time reversed in part by very 

 favorable treatment, the plants meanwhile showing improvement as regards 

 plant development and crop production. Deterioration under favorable condi- 

 tions is very gradual, but the investigators are not able to report any means of 

 permanently checking the advance of the disease when once established. The 

 question as to whether plants descended from those showing the primary stage 

 of leaf-roll disease are more susceptible to new disease influences is regarded 

 as still unsettled. 



The outward indications of deterioration show in varying degree with dif- 

 ferent varieties of potatoes. Among the sorts now common ^Magnum Bonum 

 seems to most readily acquire this disease. With this variety the investigators 

 were unable even by selection to check the decline of the stock. 



The size of the tubers is said to be no criterion of freedom from this disease 

 or of desirability in other respects for seetling purposes. 



Observations do not appear to bear out the assumption that inheritance of 

 the disease through the tubers is due to an orgnnism. It appears that along 

 with one primary stage two secondary stages occur, viz, a fungus-free stage 

 resulting from simple inheritance and a fungus-bearing form due to repeated 

 infection. The authors were not able by any treatment of the potatoes to pro- 

 duce therein the characteristic symptoms of the leaf-roll disease. 



Leaf roll of potato, G. Kock and K. Kornauth (Ztschr. Landw. Versuchsw. 

 Osterr., 15 {1912), No. 3, pp. 119-2)1, fig. i).— This is the fifth report of the 

 committee (see above) and includes studies carried on by the authors for about 

 3 years on different varieties of potatoes. 



Potato leaf roll is held, to be a parasitic disease, apparently caused by a fungus 

 of the genus Fusarium. This vegetates in the plant attacked, causing the first 

 stage of the disease. Early in its course this fungus may pass into the newly 

 formed tubers or else, through its weakening influence on the aerial portions of 

 the plant, simply produce a crop diminished in size and number of tubers. Sub- 

 sequent crops produced from these infected or simply lightened or weakened 

 potatoes will show the fungus-bearing or the fungus-free forms, respectively, 

 of the secondary stage of the disease. It was not found practicable to estimate 

 the intensity of the infection with any accuracy from the effect on the crop. 



The variety Magnum Bonum is said to be very susceptible to the disease, and 

 the deterioration through the successive generations was in this case excep- 

 tionally rapid. However, it is considered not to have been conclusively shown 

 that careful selection and favorable treatment on uninfected soil may not check 

 the decline and even show actual improvement. 



An important role is thought to be played by the soil in the transmission of 

 this disease from the old to the new plants. The question as to the duration 

 of the danger period as regards soil infection and that as to the possibility of 

 limiting or preventing such infection are regarded as still unsettled. 



