12 



SCIENCE. 



[N. S. Vol. VII. No. 158. 



changed, 6 being placed under the rays. 

 Ten minutes later b had opened slightly, 

 while a had not opened at all ; the sun by 

 this time, 6 p. m. (June 12th) , having passed 

 below the top of a western building. While 

 I intended at the time to repeat this experi- 

 ment on the following day, the result shows 

 quite conclusively, I think, that the differ- 

 ence manifested by these two plants in the 

 rapidity of opening was due to individual 

 peculiarities rather than to any influence of 

 the Eontgen rays. For while it would at 

 first appear that they exercised a slight in- 

 hibitory influence, the interchange of the 

 plants shows that this was due to the more 

 rapid response of the plant b to the influence 

 of daylight. 



In Schober's experiments the question as 

 to whether the seedlings, or any parts of 

 the plant, readily absorbed the Eontgen 

 rays was not studied. From time to time, 

 during the continuance of my own experi- 

 ments, the field was explored with the 

 fluoroscope to be certain that the rays were 

 being evolved, and also an occasional pho- 

 tograph of the hand was made as a test of 

 the' strength of the rays. Good photographs 

 were thus obtained with an exposure of 

 from four to five minutes at a distance of 

 20 cm. to 25 cm. During the close of the 

 first week's experiments the Crookes tube 

 gradually deteriorated because of the high 

 vacuum produced by prolonged use. This 

 was first manifested in the resistance ofi'ered 

 by the tube to the passage of the electric 

 current. It was also manifested in some of 

 the photographs taken at the time, the 

 plates being afiected unevenly, which indi- 

 cated that the rays were given off more 

 strongly in some directions than others. 

 This bulb was discarded on June 12th, and 

 a new one substituted on June 14th. Since 

 it is well known that the Eontgen rays pass 

 quite readily through wood the non-absorp- 

 tion of the rays by the plants might ex- 

 plain the absence of any marked influence 



upon them. Consequentlj'^, this subject re- 

 ceived some attention, and attempts were 

 made to obtain Eontgen photographs of 

 some of the plants experimented upon, as 

 well as of some other plant parts. The 

 greater number of the exposures were made 

 by placing both the sensitive plate and the 

 object inside an ordinary card box, in which 

 the plates are sold, a thin sheet of white 

 paper being placed between the sensitive 

 film and the object. A plate of a high 

 sensitometer was used. 



The first object used was an oak leaf 

 (Quercus rubra). This was exposed, first 

 for four minutes and a second time for 

 three minutes. The leaf selected was a 

 rather young and succulent one, thus being 

 more difl&cult to photograph by transmitted 

 light, but the older and firmer ones were 

 too large for the size of plate used. The 

 oak leaf was exposed for a longer time 

 than would have been necessary if the 

 method employed for a majority of the 

 photographs, described above, had been 

 followed in this case. Here, however, an 

 ordinary plateholder was used, and a black 

 rubber slide not only lay over the plate, but 

 another was placed over the leaf, which 

 was on the outside, to hold it in place. 

 While in both of these cases an outline of 

 the leaf and of the more prominent veins 

 was obtained, better results were had when 

 the exposure was made in an ordinary 

 cardboard box. Here a fairly good out- 

 line of the leaf and of its venation was 

 obtained. It is also to be observed that in 

 the shorter exposure, which is needed for 

 these delicate objects, a picture is also ob- 

 tained of the structure of the box, the thin 

 paper which is pasted on the outside, and 

 overlaps the edges, showing quite plainly. 

 Eontgen photographs of five seedlings 

 which had for several days been under the 

 influence of the rays were made. These 

 were cotton, pea, nonpareil bean and soja 

 bean, the cotton and one of the nonpareil 



