66 DEPARTMENTAL REPORTS. 



become affected was determined. Extensive studies have also been 

 inaugurated in the matter of the root rot of apple trees. Investiga- 

 tions of a disease known as crown gall Avere also begun, the object 

 being to determine the method of infection of the crown-gall organism 

 which attacks many fruit trees. This disease is becoming one of the 

 most serious enemies to the fruit growers, and its ravages extend 

 from California to the Alleghenies. It calls for verj^ radical treatment, 

 and it is believed that it can be successfully treated. 



TROPICAL LABORATORY AND INVESTIGATIONS. 



The tropical laboratory is located in Miami, Fla., and is in charge 

 of Prof. P. II. Rolfs. The work conducted at this laboratory is of a 

 miscellaneous character, and has for its principal objects a study of 

 diseases of semitroj)ical and tropical plants, the testing of plants 

 adapted to semitropical conditions, and the care of such foreign 

 plants and such hybrids as may have promise of value for southern 

 portions of the United States. During the year work has been car- 

 ried on on the root knot of the pineapple, the mango seedling blight, 

 orange blight, and other diseases. Numerous plants from foreign 

 countries have been received and planted, also seedling pineapple 

 hybrids, and seedlings of the citrus hybrids obtained as a result of 

 the plant-breeding laboratory's work. 



W^ORK ON TOBACCO. 



In October last Dr. R. H. True was detailed to the Bureau of Soils 

 to continue the study of the fermentation and handling of tobacco 

 begun by Dr. Oscar Loew. Dr. Joseph S. Chamberlain, an expert in 

 physiological work, was also detailed to give assistance. Dr. True 

 and Dr. Chamberlain spent some time in the fall and early winter at 

 Tariff ville. Conn., and Lancaster, Pa., in the study of fermentation 

 processes as practiced in the making of wrapper leaf and filler leaf, 

 respectively. Material was collected for further study in the labora- 

 torj". A thorough study of the constituents of the leaf at all stages 

 of preparation was carried on in the hope that information might be 

 gained which would shed light on the nature of the changes taking 

 place in the tobacco and increase our information concerning the 

 substances giving the desirable properties of the finished product. 



In the early winter a communication was received from a promi- 

 nent firm of eastern cigar manufacturers stating that the molding 

 of cigars was a most troublesome problem and asking for informa- 

 tion as to the cause and cure of the trouble. The matter was referred 

 to Dr. True, who was able to demonstrate that the difiiculty arose 

 from the growth of certain organisms on the surface of cigars. 

 Methods of dealing with the difiiculty were worked out in the labora- 

 tory and have been given a factory test on a large scale. The results 

 of these tests have shown that success has been achieved in con- 

 trolling this trouble. The diseases of tobacco have been handled by 

 Dr. McKenney, who has given considerable attention to a further study 

 of the mosaic disease along the lines laid down by Mr. Woods in a recent 

 bulletin on this subject. The oxidizing enzymes, which are to be con- 

 sidered tlie cause of the disease, have received sj^ecial attention. Dr. 

 McKennej^ has devised methods for the isolation of the oxidizing 

 enzymes in a state of much greater purity than has previously been 

 attained. Other investigations of tobacco diseases have been inaugu- 

 rated, but as yet it is too early to report decisive results. 



