September 3, 1915] 



SCIENCE 



315 



Most of the lower leaves were entirely dead. 

 On the under surface of the spots there was 

 apparent the characteristic red crust or scabs. 

 This crust consisted of dry bacterial ooze 

 which had come from the interior of the blade. 

 When sections of the younger spots were put in 

 a droplet of water and placed under the micro- 

 scope the bacteria could be seen oozing from 

 the infected portions in enormous numbers. 

 Pure cultures were readily obtained; some of 

 the plates contained practically no other or- 

 ganism but the causative agent. Colonies on 

 nutrient neutral agar formed rather slowly, 

 being circular, white or pearly-white in ap- 

 pearance. On putting a platinum needle into 

 a colony and lifting it, it was noted that the 

 organisms adhered in such a way as to be 

 stringy or sticljy and could be drawn out to 

 ■considerable length. 



It was at first thought that the organism 

 might be one previously described by Smith^ 

 as Bacterium andropogoni, but there seems to 

 be little doubt that the disease is due to the 

 broom-corn bacterial organism first studied 

 by Dr. Burrill, namely, Bacillus sorghi Bur. 

 This disease is one of the chief drawbacks to 

 the culture of Sudan grass on the Gulf Coast, 

 but whether it will be serious or not in the 

 Salt Lake Valley remains to be seen. During 

 the present season the month of May was very 

 rainy and humid and this probably accounts 

 for the rather serious infection of the plants. 

 Under normal weather conditions it is quite 

 possible that the disease will not prove a seri- 

 ous drawback to growing Sudan grass as a 

 forage crop. P. J. O'Gara 



Salt Lake CitTj "Utah, 

 June 28, 1915 



THE PENDULUM KEY AND ITS USE FOR EECOEDING 

 THE BEATS OP A METRONOME 



The pendulum key is a short lever, pivoted 

 at one end, and held vertically. It is so ar- 

 ranged that a slight lateral displacement of its 

 lower end causes it to make an electrical con- 

 tact. A platinum pin in this part of the lever 

 strikes against a platinum plate fastened to 



1 "Bacteria in Relation to Plant Diseases," 

 Vol. 2, 1911, Erwin F. Smith. 



the insulated piece from which the lever is 

 suspended. This simple apparatus is an ex- 

 cellent arrangement for recording the beats of 

 a pendulum or a metronome. The writer has 

 found it easy to construct such an instrument 

 by making a few additions to a key with a 

 platinum contact made by the Harvard Ap- 

 paratus Company, and used in physiological 

 laboratories to make and break a current by 

 hand. The sketch shows the key with the ad- 

 ditions to hold it in a vertical position. The 



Fig. 1. 



end of a short stud passes through a hole 

 drilled in the middle of the slate base, and is 

 held by a nut. A steel rod is screwed into the 

 other end of the stud with its axis parallel to 

 the plane of the base, and at right angles to 

 the axis of the stud. The rod is held horizon- 

 tally by a clamp fixed to the vertical rod of a 

 tripod stand. By slightly rotating the key 

 around the horizontal rod as an axis, the dis- 

 tance separating the platinum point from the 

 plate against which it strikes can be varied to 

 any desired extent. The lever can be length- 

 ened by slipping one end of a short piece of 

 rubber tubing over the handle, as is indicated 

 in the figure. The tubing acts as a spring in 

 breaking the shock of the impulse of the vibra- 

 ting rod. The apparatus is placed in such a 

 position that it receives a slight tap at the end 



