118 



Prof. J. A. Fleming. Electric Discharge [Jan. 9, 



families are also comparatively few. The families so contributing 

 are, however, among the most important and widely distributed in 

 the vegetable kingdom; as also are some of the plants they con- 

 tribute. As prominent examples may be mentioned, the Gramiwece, 

 affording the cereal grains, a large proportion of the mixed herbage 

 of grass-land, and other products; also the Leguminosce, yielding 

 pulse crops, many useful herbage plants, and numerous other pro- 

 ducts. As we have said, there does nob seem to be an unsolved 

 problem as to the sources of the nitrogen of other of our agricultural 

 plants than those of the leguminous family. Obviously, however, it 

 would be unsafe to generalise in regard to individual families as a 

 whole, from results relating to a limited number of examples sup- 

 plied by their agricultural representatives alone. Still, there is 

 nothing in the evidence at present at command, to point to the 

 supposition that there is any fundamental difference in the source 

 of the nitrogen of different members of the same family, such as is 

 clearly indicated between the representatives of the leguminous, and 

 of the other families, supplying staple agricultural products. On the 

 other hand, existing evidence does not afford any means of judging 

 whether or not similar, or allied agencies to those now under con- 

 sideration, or even quite different ones, may come into play in the 

 nitrogen assimilation of the members of other families which con- 

 tribute such a vast variety of vegetation to the earth's surface. 



We have pleasure in stating that the conduct of the investigation 

 has largely devolved upon Dr. N. H. J. Miller. He has been almost 

 wholly responsible for the analytical work, as well as for the photo- 

 graphing, by which a permanent record, not only of the above- 

 ground growth, but of the root-development of the experimental 

 plants has been secured. It should be added, that Mr. J. J. Willis 

 has materially assisted in the observation and noting on growth ; also 

 in the separation of the roots, mounting them for observation and 

 for photographing, and in noting upon them. 



II. "On Electric Discharge between Electrodes at different 

 Temperatures in Air and in High Vacua." By J. A. 

 Fleming, M.A., D.Sc, Professor of Electrical Engineering 

 in University College, London. Communicated by Pro- 

 fessor G. C. Foster, F.R.S. Received December 16, 1889. 



(Preliminary Notice.) 



It has been known for some time that if a platinum plate or wire 

 is sealed through the glass bulb of an ordinary carbon filament 

 incandescent lamp, this metallic plate being quite out of contact with 



