August 9, 1907] 



SCIENCE 



183 



so it is very easy to direct tlae blue or the 

 cadmium rays upon the face of the totally 

 reflecting prism that throws the light into 

 the substage condenser. By using two stops 

 along the curved way on which it swings 

 the illuminating apparatus can be made to 

 stop automatically at the right place to throw 

 the blue or the ultra-violet light into the 

 microscope. 



One great advantage of this system of 

 focusing is that in studying living cells it is 

 possible to do all the exploratory work and to 

 focus exactly on the details to be photographed 

 while using blue light. Only after the ad- 

 justments are made is the ultra-violet light 

 thrown on for the few seconds necessary to 

 make the photograph. This prevents injuring 

 the cells with ultra-violet light before they 

 are photographed — an injury to which many 

 delicate cells are very subject, as shown by 

 the investigations of Hertel." 



"We have made a number of other minor 

 improvements in the ultra-violet microscope, 

 such as a swing-out screen to protect the eye 

 and the microscope from the light of the 

 spark ; a pair of insulated rods to hold in place 

 the wires that conduct the high tension elec- 

 tricity from the coil and ley den jars. The 

 strength and the steadiness of the spark have 

 been improved by inserting a few inductance 

 coils in the circuit. 



None of the changes are costly and the 

 swing-out electrode holders can be made in a 

 day by any good mechanic for a few dollars. 

 On the other hand, owing to the increased 

 precision in focusing, it will no longer be 

 necessary to buy the whole series of expensive 

 monochromatic lenses. For most biologists, 

 the only one that will be needed is the highest 

 power objective of l.Y mm. focal length, which 

 alone exceeds the ordinary oil immersion lenses 

 in resolving power. 



Finally, it should be noted that the mono- 

 chromatic blue light of the magnesium spark 

 is very usefiJ. for making photographs of 



' Hertel, E., Ueber Beeinflussung des Organismus 

 durch Licht, speziell durch die chemiseh wirk- 

 samen Strahlen, in Zeitschr. f. allgem. Physiologic, 

 4: 1-43, 1904. 



microscopic mounts on glass slides with ordi- 

 nary visual objectives. In fact, no other 

 photomicrographic outfit is so convenient for 

 every day use in a laboratory that is provided 

 with an electric lighting circuit. 



The improvements of the ultra-violet micro- 

 scope here noted were described and exhibited 

 in April, 1907, at the Washington meeting of 

 the National Academy of Sciences and a few 

 days later at the Washington meeting of the 

 American Physical Society. An illustrated 

 account of the ultra-violet microscope and our 

 improvements, together with a few photo- 

 gi-aphs showing its utility in the study of 

 microscopic objects, as well as concise direc- 

 tions for setting up and using the outfit, has 

 been prepared and will shortly be published 

 as a Bulletin of the Bureau of Plant In- 

 dustry, U. S. Department of Agriculture. 

 Walter T. Swingle, 

 Lyman J. Briggs 



Bureau of Plant Industet, 

 U. S. Department op Agriculture, 

 Washington, D. C, 

 July 26, 1907 



concerning the relationship of phyllosticta 



solitaria to the fruit blotch 



of apples 



During the past four years, the writer has 

 been collecting specimens of apple leaves and 

 fruits having spots on them caused by fungi. 

 Eecently these specimens were examined to 

 determine what fungi are present in the spots. 

 As a result of this examination, it was found 

 that a fungus which caused spots on the 

 leaves and fruits of a wild crab-apple (Mains 

 coronaria (L.) Mill.) also caused spots on the 

 petioles and underside of the midribs of the 

 leaves and of the fruits of the common apple 

 {Mains Mains (L.) Britton), a condition that 

 might be anticipated. 



The spots on the leaves of the crab-apple 

 are either brown or white, about a millimeter 

 in diameter, and with a distinct, raised, brown 

 or purplish border. In the center of the spots 

 there is a single, minute, black pycnidium 

 (rarely more than one). The white spots may 

 be older than the brown ones, both occurring 

 side by side on the leaf. The spots on the 



