ANNUAL REPORT, 1946-47 21 



Parallel with the soil cultures was a series of solution cultures, at the same 

 temperatures and with the same varieties of tobacco. The solution, Shive's R5S2 

 at 1.75 atm., consisted of KH2PO4, Ca(N03)2, MgS04, with FeS04 as a source 

 of iron. Frenching did not appear at either the high or the low solution tem- 

 perature. The failure to induce frenching at the high solution temperature pre- 

 cludes the suggestion that root metabolism at a high temperature could be a 

 cause of frenching. The nutrient solution was altered in several ways and vari- 

 ous forms of iron were used in an effort to induce frenching, all with negative 

 results. Soil extracts were obtained from frenching soils bj' mixing soil with dis- 

 tilled water and filtering. These were added to nutrient solutions but caused 

 no symptoms of frenching. 



Frenching has always been obtainable with a compost soil. To test a field 

 soil, two tobacco field soils taken in the autumn were used for culture media 

 parallel to the compost soil. At 95° F. the compost soil produced frenching in 

 14 days; field soil No. 1 in 20 days; and field soil No. 2 in 58 days in one plant 

 of four. The field soils had been stored until February and were quite dry. Sub- 

 sequent tests showed that air-drying of soil eliminated the ability to cause french- 

 ing. Autoclaving the soil for one hour at 15 pounds steam pressure also pre- 

 vented frenching. 



Tests made on frenched leaves showed a large amount of nitrates when it was 

 known that there was an ample supply of nitrogen in the soil. Tests for major 

 and minor elements, made by the floating disc method, showed a response to 

 iron. Leaf analyses of frenched leaves showed a low amount of iron compared 

 with normal leaves. It appears that a lack of iron in the plant seriously inter- 

 fered with a proper utilization of nitrates. The osmotic concentration of the cell 

 sap of leaf tissue of frenched leaves was above normal; 14 atmospheres for frenched 

 leaves and 9 atmospheres for normal leaves. A histological examination of leaf 

 tissue showed a lack of palisade tissue and spongy parenchjma in the frenched 

 leaves. 



Experiments in which iron was mixed with the soil in the forms of FeS04 

 mixed with peat and FeP04 mixed with peat resulted in the complete prevention 

 of frenching with the FeS04-peat mixture. Results were not so good with the 

 FeP04-peat mixture, and practically no control was obtained when either of 

 these chemicals and peat were used separately. 



When a little soil that had caused frenching was mixed with an autoclaved soil 

 frenching was induced at 95° F. but not at 70° F. No frenching occurred in an 

 uninoculated autoclaved soil. 



The evidence now at hand indicates that at a soil temperature of 95° F. there 

 is an effect on the soil flora which causes oxidation of iron to an unavailable form, 

 and this oxidation takes place more rapidly than the reducing reactions which 

 would normally maintain some iron in a ferrous form available for intake by the 

 plants. Frenching results from a deficiency of available iron and may be pre- 

 vented by supplying an excess of iron in the form of a ferrous humate made by 

 mixing FeS04 with peat. 



Resistance to Fusarium dianthi Prill, et Del., the Cause of a Serious Carna- 

 tion Wilt Disease. (E. F. Guba, Waltham.) The following varieties of carna- 

 tions have been crossed and self pollinated in the long effort to develop desirable 

 commercial types resistant to Fusarium Branch Rot: 



Dorothy Napier Helen Hussey Millers Yellow 



Puritan John Briry Woburn 



Maine Sunshine Elizabeth Rowe Paragon 



My Love Georgina Hazel Draper 



Eleanor King Cardinal Tom Knipe 



