DISEASES OF PLANTS. 955 



is of coiuparativcly raiv (icciirrciicc in Ohio, and he pdints oiil llic rclationshii) 

 I)et\veon tbe tKrurreiice of this disease and the cliiiiatic conditions dnrinjj; the 

 f,'i-o\vin.sir season. It appears that I'lii/loitlitliora uifcstinis is prevalent in Ohio 

 only durin;; seasons of abnormally low teniperatnre acconi|ianied with an 

 altnudanee of moist nre. When the tenijierature is liif^h the fnngus does not 

 seem to he able to develoi), Init there ai)pears to be cyclic periods of low sum- 

 mer temperature when an outbreak of late blight of potatoes may be expected. 



fn relation to the downy mildew of the cucumber, the conditions are just the 

 I'everse, as it requires a high temperature for the development of the fungus, 

 and the outbrealvS of the disease on cucumbers and allied plants in Ohio liave 

 coincided with seasons that were warmer tlian the average. A cool season 

 results in a late development of the fungus, and apparently the optimum tem- 

 peratures for the development of I'lasmopara cuboinis are probably near the 

 summer maximum in Ohio. The author believes that this fungus, for whicli no 

 ('iospores are Icnown, is in all probability propagated by the conidia spreading on 

 wild and other cucurbits, and that the advance is limited by the summer tem- 

 peratures. 



Plans for procuring' disease resistant crops, H. L. Bolley (Proc. Soc. Prom. 

 .If//'. /Sc/., 28 {1907), pp. 107-1 l.'f). — A description is given of the author's 

 experiments with wheat, flax, and potatoes to secure strains immune to disease. 

 The method in brief is to provide all known conditions for the disease in order 

 to eliminate the weak plants. It is believed that this procedure will at least 

 bring about conditions for a study of the principles underlying what is known 

 as resistance to plant diseases. 



A disease of chicory, H. Blin (Rev. Hort. [Parish, 80 (1908), No. 1, pp. 

 16-18). — Attention is called to a disease of chicory which is said to be espe- 

 cially destructive in the process of blanching. This disease, which is caused 

 by Sclerotina libertiana, is probably present when the plants are placed to 

 blanch. Basing his opinion on the effect of a copper sucrate fungicide on other 

 jilants, the author believes that this would be efficient in reducing the loss. 



Potato diseases in 1907, W. J. Morse { Maine St a. Bui. 149, pp. 287-330, pis. 

 Jf, (Ujni. 1). — The prevailing conditions in 1907 are said to have been favorable 

 for the development of potato diseases in Maine. A series of investigations 

 was carried on as to different measures for the protection of potatoes, the 

 results of which are given at some length. 



A number of dust sprays were compared with ordinary Bordeaux mixture 

 for the prevention of potato blight, with results showing that Bordeaux mix- 

 ture as usually prepared was decidedly more efficient than any of the dry 

 or commercial preparations tested. 



The relative elticiency of light and heavy spraying was determined, plats 

 being double sprayed, that is, sprayed in opposite directions on the same dates, 

 and comparisons made witli single sprayings. The yields from 6 heavy spray- 

 ings, carried on in 2 different localities, were 45 bu. per acre in one case and 

 77 bu. per acre in the other more than the best yields of the remaining plats. 



In continuation of previous experiments with formaldehyde gas for the 

 prevention of potato scab (E. S. R., 18, p. 1140), the author treated at one 

 time seed potatoes sufficient for the planting of 20 acres. Tliese were arranged 

 in slat bins in a tight inclosure and sul)jected to gas given oft' by the applica- 

 tion of 4 pints and 1 oz. of formaldehyde to .31 i oz. of potassium ]iermanganate. 

 Comparisons made witli tubers soaked in a solution of formaldehyde confirmed 

 previous conclusions regarding the use of formaldeliyde gas for the treatment 

 of large quantities of seed potatoes. T.ittle injury followed the use of formal- 

 dehyde gas, but the author calls attention to the necessity of having the 

 43854— No. 10—08 5 



