18 MASS. EXPERIMENT STATION BULLETIN 369 



mosaic, it was found that out of 2129 plants grown on the plot which contained 

 only the roots of the preceding tobacco, 12, or .61 of one percent of all the plants, 

 had developed mosaic; and out of 1232 plants grown on the plot which contained 

 only the tops of the preceding tobacco, 10, or .81 of one percent of all the plants, 

 had mosaic. 



In the tobacco grown for use in ascertaining the extent to which mosaic inoculum 

 might be disseminated from diseased to nondiseased tobacco plants by means of 

 cultural practices, 5 percent of all the plants were inoculated artificially by hand, 

 but otherwise the tobacco was treated as tobacco grown for commercial purposes 

 would ordinarily be treated. Counts of mosaic-diseased plants were made just 

 before topping and just before harvest. From counts made just before topping 

 it was found that out of 2122 plants grown on the plot, 191 or approximately 

 9 percent of the plants had developed mosaic, or 4 percent more than the number 

 of plants which had been inoculated artificially by hand. Counts made just 

 before harvest showed all the plants to have mosaic. 



The tobacco grown for control purposes and used for control in connection with 

 both experiments described above, had no mosaic-diseased plants. 



DEPARTMENT OF ANIMAL HUSBANDRY 



Victor A. Rice in Charge 



The Effect of Feeding a Vitamin A Concentrate on Growth and Reproduction 

 in Dairy Cattle. (J. G. Archibald and C. H. Parsons.) This project has been 

 completed and the results have been published in Bulletin 357. 



The Effect of Complex Mineral and Vitamin Mixtures on Milk Production, 

 General Health, and Reproductive Efficiency in Dairy Cattle. (J. G. Archibald.) 

 The data have been correlated and summarized, and preliminary reports have 

 been prepared on two of the three long-time feeding trials conducted under this 

 project. Data from the third trial are in process of correlation and summary. 

 Results from the two studies which have been completed do not show any benefits 

 from the feeding of the two proprietary mixtures in question. 



A Study of the Mineral Elements of Cows' Milk. (J. G. Archibald and C. H. 

 Parsons.) Supplemental iron in the form of iron ammonium citrate, fed to a 

 group of eight cows in the college herd during the winter of 1938-39 did not 

 increase the average iron content of their milk. In fact the tendency was towards 

 a decrease. Large variations were noted in the iron content of the milk between 

 individual cows at any given time, or between samples from the same cow at 

 monthly intervals. Both of these types of variation were noted irrespective of 

 whether supplemental iron was being fed or not. The iron content of most of 

 the samples was of the order of 0.5 mg. per kilogram of milk or less, although there 

 were a few samples where it ran as high as 1.0 mg. per kilo, or even higher. 



Some dissatisfaction was experienced with the method used for determining 

 iron and certain refinements and modifications were introduced which gave more 

 uniform values for the samples obtained in the latter part of the season. Because 

 of this and also because the trend toward a decrease in the iron content of the 

 milk when additional iron was fed does not seem logical, it has been decided to 

 repeat the work during the barn-feeding season of 1939-40. Somewhat larger 

 amounts of supplemental iron are being fed this year. 



Investigation of the Merits of Legume and Grass Silage for Massachusetts 

 Agriculture. (J. G. Archibald and C. H. Parsons.) Results from this project 

 to the end of 1938 together with findings of other workers applicable to conditions 



