CALIFORNIA. 103 



effect of holding down the winter temperature, reducing sunshine, 

 changing the time of planting, and the influence of similar other 

 agencies were also studied in this connection. 



A lot of seedling walnuts from various parts of the State, studied 

 with reference to type, were budded with English walnuts to de- 

 termine the effect on the stock, and observations were made on crosses 

 of oak on Avalnut to ascertain whether the " walnut oaks " found 

 gi-owing wild in parts of the State are the result of a cross or must 

 be otherwise accounted for. This work w^as in progress at Berkeley 

 and near Los Angeles. 



The work on Nicotiana hybrids was followed according to the 

 original plan. About 1,200 individuals representing different sorts, 

 types, and strains have now been produced in these experiments, 

 which have been conducted to some extent in cooperation with this 

 department. In the first generation close observations were made for 

 the purpose of adding to our knowledge of the law of hybrids and 

 if possible securing results of practical value in tobacco breeding. 



The investigations on the control of the scales of the citrus trees 

 were largely confined to tent fumigation with cyanid. The leak- 

 age from common tents was determined and the dose for fumigating 

 for young black, red, and purple scales, allowing for leakage, was 

 worked out. Xew and simple methods and apparatus were devised 

 for scheduling trees in the field and thus determining the size of 

 tree and the tent room and material required for successful fumi- 

 gation. The effect of humidity, temperature, wind, and similar 

 factors on the efficiency or leakage was also taken into consideration. 

 The study of the life history and classification of the citrus scales 

 was carried on as a separate project, and breeding work was pursued 

 with a view to turning yellow scales into red and vice versa in the 

 successive generations by change of environment and other influences. 



A thorough study was made of the life history of the Argentine 

 ant, its manner of spreading, and methods for its control. Good 

 results were secured from the use of bait treated with arsenical 

 poisons, and with cresol and kerosene in combating the insect. It 

 was observed that the Argentine ant spread slowly as the queens do 

 not mate in the air, but owing to the large number of queens it is 

 ver\^ prolific. The facts seem to indicate that the extennination 

 of the ant is a possibility, and work was begun to determine the 

 practicability of stamping it out in a given locality. As the re- 

 search features of this investigation have now passed, the work will 

 be discontinued as a research project. The study on the toxicity 

 of the various arsenical poisons used as insecticides was intemipted 

 by the appearance of the Argentine ant but will be taken up again. 



The artificial immunization of cattle against tuberculosis was con- 

 tinued on the farm at Davis, and some of the results were reported 



