202 



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II, 192 



Letters to the Editor. 



The luiilcf (ti>r< /w! /v.',/ J::n:.rif 

 opiiiicus (• 1 

 cm he i/thit 



tilt' -.i.'rilos r'/, u'l^iltii DiiuniMt 

 this or (iHV otiirr />iir/ of N' \ 1 1 1 , 

 titkrn of iiiii'rtvmoits ciufnnunuiitions. 1 



for 

 is 



Photographic Plates for the Extreme Ultra-Violet. 



In recent years there 1ul\ e been a number of 

 attemptvS to improve the photographic methods, 

 perfected by Schumann, used in the investigation 

 of the ultra-violet, so far without any very striking 

 results. 



Recently Mr. David Mann and I have been making 

 some experiments with the daguerreotype process. 

 The results, though interesting, are so far of no great 

 practical value. It is not difficult to prepare a surface 

 which will be very sensitive in the region about 

 wave-length 1850 A.U., and on two or three occasions 

 we have obtained records extending to wave-length 

 584 A.U., but in general the behaviour of the plates 

 in the extreme ultra-violet is capricious and un- 

 satisfactory. 



Duclaux and Jeantet {Journal de Physique, ii., 

 1921, p. 154) have described a way of " Schumann- 

 ising" an ordinary dry plate by treating it with 

 sulphuric acid, and recently Aston has referred to the 

 same process. M. Duclaux has been so kind as to 

 send me some specimens of the results he has obtained. 

 He informs me, however, that he prefers another 

 method which he and his colleague have discovered, 

 described in their article just cited. His experi- 

 ments were confined to the region of the spectrum 

 which may be investigated with a quartz prism 

 spectrograph ; I have continued them into the 

 extreme ultra-violet. 



The procedure is extremely simple. A fast com- 

 mercial photographic plate (I have employed a 

 " Seed 30 ") is coated with a thin film of a colourless 

 paraffin oil. It is then exposed in the usual way in 

 a vacuum spectroscope, the oil is removed with 

 acetone and the plate is developed. The results are 

 nearly, though not quite, as good as those which I 

 have obtained with the most sensitive Schumann 

 plates prepared according to the old method ; it is 

 quite easy to get a record of the strong helium line 

 at X584 A.U. 



The success of the process evidently depends on 

 fluorescent action ; I have tried a number of different 

 kinds of oil, and I find that " Nujol," a very pure 

 oil sold in this country for medical purposes, yields 

 good results. 



I feel sure that this discovery of Duclaux and 

 Jeantet will prove a real blessing to all spectro- 

 scopists who work in the extreme ultra-violet. 



Theodore Lyman. 



Jefferson Laboratory, Harvard University, 

 June 28. 



The Presence of Urease in the Nodules on the 

 Roots of Leguminous Plants. 



After the discovery of urease in the Soya bean by 

 Takeuchi in 1909, the presence of this remarkable 

 urea-splitting enzyme -was soon recognised in the 

 seeds of many leguminous plants. On the other hand, 

 while the occurrence of the enzyme in seeds from 

 widely different varieties of plants has been recorded 

 in recent years, its absence from the seeds of several 

 Leguminosae has also been noted. 



NO. 2806, VOL. I 12] 



So far as we have been able to ascertain, tli 

 peculiar root iioilnlfs of leguminous plants have not 

 hitherto been t( t' il for urease. Experiments carrie<! 

 laboratory in conjunction with Mr. J. V. 

 '• revealed the presence of tlie particular 

 III/ III' i;i ;ill the cases examined. Crushed n^^ ' ' 

 taki n from tin- well-washed rootlets of Trij 

 procunibiHs, T. pratensr 7 -""pens, Vicia samu, 

 Medicago sativa, Galega ' various lupins, and 



the garden pea, were placi.. ... ^^^rately in a two per 

 cent, solution of urea (sterilised by saturation with 

 toluene) to which a few drops of neutral phenol-refl 

 solution li;i(I heen added as indicator. A purple-re 

 colour, due to ammonia generated from the d' 

 composition of urea, was gradually developed in tl 

 solutions, after they had been maintained at 55° fi 

 about an hour. Several control experiments showi 

 that ammonia was not generated in the absence < 

 urea, and that the solution of the latter alone did nc^v 

 change the colour of the indicator under the abo\e 

 conditions. Also, rootlets not bearing nodules, and 

 roots taken from plants belonging to several different 

 natural orders, failed to give any evidence of tl 

 presence of urease. Judging from qualitative exper 

 ments, nodules from the white and the yellow tret 

 lupin appeared to be the most active of those examined 



From these observations it must be concluded that 

 the nodules on the roots of leguminous plants possess 

 an additional function to the one which they hav^ 

 been known to perform since Hellriegel's discover^ 

 While we have not found urease in any roots devoi^^ 

 of nodules, clear evidence was obtained of its presence 

 in the cylindrical tuberous growths developed from 

 the rootstock of the lesser celandine {Ranunculus 

 Ficaria). This is the only case so far in which the 

 enzyme has been detected in the adjunct of a root 

 outside the leguminous family of plants. 



An interesting demonstration of the presence of 

 the enzyme can be made without crushing the 

 nodules. The entire root cut from a young pea plant, 

 or preferably from a young lupin, as it usually carries 

 larger nodules, is immersed in a solution of urea 

 containing a liberal supply of the indicator (neutral 

 phenol-red). The action of the enzyme is allowed 

 to continue until the solution has attained a rich 

 purple-red colour, which of course requires a much 

 longer time than if the nodules had been crushed. 

 The root is now removed from the solution, rinsed for 

 a few moments under the tap and then placed in 

 water to which a few drops of the indicator hav-e 

 been added. The diffusion of alkaline solution from 

 nodules into the outer liquid can be readily observed 

 by the zone of colour which forms in the solution 

 directly round the nodules. 



While the first part of this experiment illustrates 

 the relatively feeble activit)- of the nodules in situ, if 

 the root be now washed in running water until the 

 colour of the indicator is no longer affected, it will be 

 found that when immersed again in a solution of 

 urea the rate at which the latter is decomposed will 

 be much greater than when the nodules were tested 

 originally. This obviously suggests that urease is 

 produced within the nodules during contact with 

 the urea solution. Under natural conditions the 

 micro-organisms present in the nodules are probably 

 concerned in the generation of the enzyme as required. 

 In our experiments the antiseptic power of toluene 

 was apparently insufficient seriously to affect their 

 activity. Pending a more extended investigation 

 of the subject, our preliminary'^ observations seem 

 worth recording. 



E. A. Werner. 



University Chemical Laboratory-, 

 Trinity College, Dublin. 



