ANNUAL REPORT, 1945-46 23 



Breeding (selfing and crossing) was handicapped by the failure of some of these 

 varieties to produce pollen and by the production of pollen of others during a 

 limited season. Seed from selfing and crossing has been obtained. More success 

 is anticipated in another season. 



Combinations of Fermate and Arasan with hormone powders in the ratio of 

 10 percent fungicide and 90 percent hormone powder, as a treatment of the basal 

 end of cuttings before they are inserted in the sand, combined disease control 

 with better rooting. Similarly, either Fermate or Arasan combined with talc in 

 a 10-90 ratio gave good control of branch rot and was not harmful to rooting. 

 Comparable results were secured with concentrated Fermate and Arasan. Im- 

 mersion of the cuttings for 15 minutes in a 1-1,000 solution of potassium perman- 

 ganate was relatively unsatisfactory. The tests were based on the varieties 

 Eleanor, Olivette, and King Cardinal. 



Control of Seed Decay and Damping-off of Vegetable Seedlings with Seed- 

 borne Chemicals. (E. F. Guba, Waltham.) Since the publication of Bulletin 

 394, "Control of Damping-off of Vegetables by Formaldehyde and Other Chem- 

 icals," in June 1942, further seed treatment trials have been made each year. 

 As a result of these studies, Spergon (tetrachloro-parabenzoquinone) is given 

 wider prominence, and Arasan (tetramethyl-thiuram-disulfide) is added and 

 recommended for most vegetable seeds except crucifers. The chemical 2, 3- 

 dichloro-1, 4-napthoquinone (Phygon) is another valuable addition. Revisions 

 in seed treatment recommendations have been made, based on these studies. 



Tobacco Frenching Induced by High Soil Temperature. (L. H. Jones.) After 

 Havana Seed tobacco plants had become established in vigorous growth at a 

 soil temperature of 70° F., the soil temperature was raised to 95° in one half the 

 series, while the other half was left at 70° as a check. Frenching eventually de- 

 veloped in all the plants at the high temperature and the check plants remained 

 normal. 



The fact that the plant containers used in previous experiments were of gal- 

 vanized iron suggested the possibility of toxicity from zinc compounds made 

 soluble by a high moist temperature in the presence of soil constituents. To 

 eliminate this possibility, one-gallon glazed crocks were set into the two-gallon 

 galvanized iron containers. Lime in the form of calcium hydroxide and boron 

 in the form of borax were added to a portion of the series. The frenching symp- 

 toms appeared in all plants at 95° F. soil temperature and were absent at 70° F. 

 regardless of other treatment. Prior to the appearance of extreme symptoms of 

 frenching, leaves intermediate In development between normal and truly frenched 

 exhibited an interveinal chlorosis best described as pinhead mottling. When- 

 ever this occurred, terminal growth decreased and the tip of the plant gradually 

 developed a rosette of typically frenched leaves. There was considerable time 

 lag between exposure to the high soil temperature and appearance of the pinhead 

 mottling. Plants in the glazed containers were the first to show the symptoms, 

 21 days being the minimum time and this in the months of February and March. 

 Limed soil produced the largest plants and delaj^ed the appearance of the symp- 

 toms, the time lag being 35 days. Borax delayed the appearance of symptoms 

 still longer, 57 days, but did not reduce their severity. The cessation of ter- 

 minal growth as one of the symptoms of frenching sometimes released the In- 

 hibitory influence in the development of buds in the axils of the leaves. When 

 growth In the axils did occur on frenching plants, it was either an elongating 

 axillary shoot with frenched leaves, eventually producing a rosette comparable 

 to that on the original terminal shoot, or simply a rosette of frenched leaves in 

 the axil. The elongating shoots were nearer the tip of the plant and the sup- 

 pressed shoots were nearer the base. 



