ANNUAL REPORT, 1935 23 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in Charge 



Control of Greenhouse Vegetable Diseases. (E. F. Guba, Waltham.) 

 Since the last report the F 3 generation of lines of the original crosses of the 

 Red Currant Tomato with the Belmont, Success, and Break O'Day varieties, 

 selected for resistance to the leaf-mold fungus Cladosporium fulvum Cke., were 

 grown. In this growing, certain resistant lines were crossed with the varieties 

 Field Station, Lloyd, and Baltimore to improve fruit size. In the F, growing 

 of these hybrids 49 selections were made for the F 2 growing which is now under 

 way. 



The disinfection of the greenhouse interior with chemicals between crops 

 offers a real problem. The burning of sulfur has serious objections. The com- 

 bustion products of burning sulfur react with zinc wires, zinc white paints, and 

 iron pipes and construction to form soluble metallic sulfates which on dripping 

 on the plants of the succeeding crop cause an epidemic of burning. With the 

 cooperation of Dr. E. B. Holland of the Department of Chemistry, the action 

 of the fumes of burning sulfur on various white pigments used in paint are 

 being studied. 



Formaldehyde gas generated from liquid formaldehyde (37 percent) with 

 potassium permanganate is lethal to spores of Cladosporium fulvum Cke., but 

 at dosages and costs prohibitive in practice. Studies are in progress concerning 

 the merit of hydrocyanic acid gas and of naphthalene as possible substitutes 

 for sulfur, either of which, if successful, would greatly simplify the practice of 

 cleaning up infestations of parasites between greenhouse crops without the 

 harmful action on painted and metal surfaces or the production of plant poisons. 



Vegetable Seed Treatments. (C. J. Gilgut, Waltham.) Dry chemical 

 seed treatments were limited to two field trials of copper oxides, zinc oxide, 

 Vasco, and Semesan. An excess of powder was added to the seed. The surplus 

 powder was then screened off before planting. Red copper oxide gave the best 

 stand of lettuce, and zinc oxide was almost as good. Zinc oxide proved best 

 for cabbage, radish, carrot, and cucumber. Vasco, a commercial product con- 

 taining zinc oxide, proved superior with turnip and spinach, although with 

 spinach no significant contrast was shown between Vasco and zinc oxide. 

 Semesan gave the best results with peas, beets, corn, and onion, although with 

 beets red copper oxide was about as good, Red copper oxide which had turned 

 black was distinctly injurious in these trials. 



These trials contributed to the evidence that zinc oxide has considerable 

 value in the treatment of vegetable seed for the control of damping-off . 



Causes and Control of Decay of Winter Squash in Storage. (E. F. 



Guba and C. J. Gilgut, Waltham.) This project was suspended during the 

 senior author's leave of absence. Temperature records are being kept in 

 several storages for the storage season of 1935-36. 



Up to this writing squash have kept unusually well in contrast to poor keeping 

 up to this time in other years. Observations seem to indicate that the unusually 

 dry growing season is a major contributing factor. To this may be added the 

 dry, cool weather conditions prevailing after harvest, which have aided in the 

 maintenance of dry storage conditions. 



Carnation Blight. (E. F. Guba, Waltham.) Cooperative experiments 

 designed to demonstrate the effect of Bordeaux on carnations as a protection 

 against blight caused by Allernaria dianthi S. & H. have been arranged with 



