340 MASS. EXPERIMENT STATION BULLEETIN 247 



Factors Influencing the Heading of Greenhouse Lettuce. {X. A. Tied- 



jens). Because of the decline of the greenliouse liead lettuce industry, a 

 study of factors affecting the heading of lettuce has been discontinued. 



The breeding of a mildew resisting, hard heading type for winter grow- 

 ing conditions has resulted in a selection that promises to take the place 

 of the Belmont and May King varieties. The selection was made from a 

 cross between Belmont, a firm heading type but susceptible to mildew, and 

 May King, a large loose-heading, mildew-resistant type. The variety has 

 been named Bel-May. It is not as resistant to mildew as May King, but 

 a firmer heading type for winter conditions. Apparently, resistance to 

 mildew is correlated with the more open type of growth shown by the 

 May King variety. 



The new variety is being grown by several growers for a commercial 

 test and is showing considerable promise. 



The Improvement of Beets Through Selection of Roots and Seed Pro- 

 duction. (V. A. Tied.jens). Cooperation with Wyman Brothers of Ar- 

 lington, Mass., h;;s made available a fine selection of beets. 



The Improvement of Carrots Through Selection of Roots and Seed Pro- 

 duction. (V. A. Tied.jens). A fine selection of Hutchinson Carrot has 

 been develoi)ed, and last year over 200 pounds of the seed was distributed 

 to growers. This is now in the hands of the Seed Committee of the 

 Boston Market Gardeners Association who are merchandizing the seed. 



DEPARTMENT OF VETERINARY SCIENCE 



J. B. Lentz in Charge 



The Standardization of Avian Diphtheria, Roup or Bird Pox Virus and 

 Vaccines with Special Reference to Improving the Treatment of the 

 Disease. (N. J. Pyle.) Since the publication of Technical Bulletin No. 14 

 in June, 1928, progress has been made in the study of the duration of 

 the immunity produced by the cutaneous vaccine and in the results of its 

 adininistrati<m to birds as it may affect e^fi: production, body weight, and 

 temperature. It is planned to make further studies on the standardiza- 

 tion of the vaccine. 



Laboratory Service — Pathology. (G. L. Dunlap.) From December I, 

 1926 to ,hine 15, 1927, 2,422 specimens were examined. These included 

 1,272 chicks, 95 adult chickens, 3 ducks, and 1,052 miscellaneous. From 

 June 15, 1927 to June 30, 1928 this service was suspended, except for ex- 

 aminations of urgent material, which included 578 miscellaneous speci- 

 mens. On July 1, 1927 it was resumed, with a fee of $2.00 for each 

 examination. Since July 1, 68 examinations have been made with a total 

 of 160 speciTuens. These include 106 chickens, 1 turkey, 6 foxes, 5 

 pigeons, 1 rabbit, 2 feed samj^les, and 39 miscellaneous specimens. 



Poultry Disease Elimination Law. (W. R. Hinshaw and E. F. Sanders). 

 The progress made in the control of Salmonella pullorum infection (Bacil- 

 lary White Diarrhea) is summarized in Control Series Bulletins 39 and 

 43, which record the results of agglutination testing for the 1926-27 and 

 1927-28 seasons. 



During the 1926-27 season, 127,327 tests were made in 249 flocks and 

 114 of these flocks, comprising 40,269 birds, were reported negative to the 

 agglutination test. During the 1927-28 season, 232,091 tests were made 



