610 



SCIENCE 



[N. S. Vol. XLIV. No. 1139 



the theorem employed by Professor Hunting- 

 ton involves a physical principle not explicitly 

 stated by him, namely that matter consists of 

 individual particles, each of which preserves 

 its identity and its mass throughout all phys- 

 ical or chemical changes. 



Those who believe that mechanics should be 

 regarded as a physical science rather than a 

 branch of pure mathematics will probably 

 agree that in elementary instruction it is less 

 important to build up a logical framework 

 than to help the beginner to appreciate the 

 physical meaning of dynamical laws. 



L. If. Hoskins 



Stanford University, 

 September 16, 1916 



FLASHING OF FIREFLIES 



To the Editor of Science : The notes by 

 Mr. Edward S. Morse in Science for February 

 4 and September 15, 1916, on fireflies flashing 

 in unison, have been of very great interest 

 to the writer, in connection with his studies 

 of the light-emission of American Lampyrida?, 1 

 and during the course of these observations he 

 has constantly been on the watch for synchro- 

 nous flashing of the type reported by Mr. 

 Blair and by Mr. Morse. There seems to be 

 no doubt that it is a fairly frequent, if not a 

 constant, method of light-emission among cer- 

 tain tropical (mainly oriental) Lampyrids, 

 but instances of it in our North American 

 species must be fortuitous, at least in this 

 locality. The writer's observations so far 

 made have been on Pyractomena borealis, P. 

 lucifera, P. angulata, Photinus pyralis, P. 

 consanguineus, P. scintillans, P. marginellus, 

 P. castus and Photuris pennsylvanica. In 

 most of these there is now no doubt that the 

 photogenic function serves as an attraction 

 between the sexes for mating, and synchro- 

 nous flashing of a large number of individ- 

 uals would seem to be of such a nature as to 

 interfere with this function of the light. 

 Among the species studied, there would ap- 



i Canadian Entomologist, 1910, Vol. 42, p. 357 ; 

 1911, Vol. 43, p. 399; 1912, Vol. 44, pp. 73, 309; 

 Zeitschrift fuer wissenschaftliche Insektenbiologie, 

 1914, Vol. 10, p. 303. 



pear to be a possibility of anything approach- 

 ing synchronous flashing only in Photuris 

 Pennsylvania, whose lighting habits it has 

 been found difficult to follow accurately. 

 On one or two occasions during the past 

 summer observations were made by Mr. 

 H. S. Barber, of the National Museum, and 

 the writer, of what appeared to be the alter- 

 nate illumination of adjacent trees in which 

 this species was present in abundance, but it 

 was soon evident that while at a given instant 

 one tree may have been more highly illumi- 

 nated than the other, there was nothing ap- 

 proaching periodicity in the phenomenon, and 

 no continuation of it was noticed. Of course, 

 special conditions of temperature, moisture, 

 air currents, etc., might influence these insects 

 in such a way as to produce synchronous flash- 

 ing, but although especially watched for, we 

 have been unable to secure an observation of 

 it. If any other observations of this char- 

 acter have been made on North American 

 species of Lampyrids, the writer would be 

 very glad to hear of them. 



In regard to the synchronous head move- 

 ments of ants, referred to by Mr. Morse as 

 having been reported by Cox, it may be noted 

 that one of our common web-worms exhibits a 

 very similar conduct, a stimulus, such as a 

 shadow passing over the colony, being suffi- 

 cient to cause all of the caterpillars to jerk 

 the head and forward segments from side to 

 side, the great majority of them to the same 

 side at the same time. 



F. Alex. McDermott 

 Washington, D. C, 

 September 20, 1916 



OCCURRENCE OF YELLOW LEAF RUST OF 



WHEAT (PUCCINIA GLUMARUM) IN 



THE SALT LAKE VALLEY, UTAH 



On June 23, 1915, the writer and one of his 

 assistants, Mr. W. "W. Jones, collected an ap- 

 parently new rust on wheat in several fields 

 north and west of Ogden, Utah. It was noted 

 that the infection was very serious and in some 

 instances the fields had the appearance of 

 suffering greatly from drouth. A careful ex- 

 amination, however, showed that this condi- 



