966 



SCIENCE 



[N. S. Vol. XXXII. No. 835 



ber of species and the relationship of every 

 genus of vascular plants (" Phanerogamen 

 und Pteridophyten "). Whether the remain- 

 der of the vegetable kingdom is to be covered 

 in this manner by the author is not stated, 

 but we may here express the hope that this 

 will be done. 



By leaving out synonyms, and by printing 

 two columns on each page the author and 

 publisher are able to bring the whole book 

 into 260 pages, including a four-page " Uber- 

 sicht der Familien " and a three-column, six- 

 teen-page index. The sequence of families is 

 essentially that of Engler and Prantl, re- 

 versed, and the older ideas as to the limits of 

 families are generally adopted. Thus we find 

 Compositae undivided, as also Convolvulaceae, 

 Ericaceae, Rosaceae and Oupuliferae, while 

 on the other hand we have Leguminosae di- 

 vided into Mimosaceae, Caesalpiniaceae and 

 Papilionaceae, and Sapindaceae, into Sapin- 

 daceae, proper, Eippocastanaceae and Acer- 

 aceae. The number of species is given for 

 each genus, tribe, family, series, class and 

 phylum, and for the larger groups the num- 

 bers of genera and families are given. We 

 know of no other work in which numerical 

 relations have been so fully worked out as in 

 this little book. Incidentally we find in these 

 latest estimates that the number of known 

 species of plants' is considerably larger than 

 has been supposed, and we have the data for 

 making the following changes in the table as 

 given on the pages cited: 



Pteridopliyta 

 Calamophyta 

 Lepidophyta . 

 Cycadophyta , 

 Strobilophyta 

 Anthophyta . 



3,820 species instead of 2.500 



2.4 " " 20 



701 " " 900 



137 " " 140 



386 " " 450 



.132,584 " " 110,000 



The latter are divided into: Monocotyle- 

 dons, 23,747 species instead of " about 20,000," 

 and Dicotyledons 108,837 instead of " about 

 90,000." These corrections bring the total 

 number of species of plants now known up to 

 somewhat more than 233,000 (instead of 

 210,000). Charles E. Bessey 



The University or Nebraska 



•See Science for November 11. 1910, pp. 669- 

 670. '^^ 



SOCIETIES AND ACADEMIES 



THE PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 0S4th meeting of the society was held on 

 November 19, 1910, Vice-president Rosa in the 

 chair. Three papers were read: 



Record of Lightning Stroke at Cheltenham Ob- 

 servatory: R. L. Faeis, of the Coast and Geo- 

 detic Survey. 



This paper gave a description of the occurrence 

 of a lightning discharge which struck the Chelten- 

 ham magnetic observatory during the prevalence 

 of a severe thunder-storm on the evening of July 

 12, 1910, and the effect it produced upon the self- 

 recording magnetic instruments. Lantern slides 

 of the photo-magnetic records during the thunder- 

 storm were exhibited, and tables of base-line 

 values for periods of time before and after the 

 occurrence of the disturbance which showed that 

 no permanent displacement of the magnets had 

 been produced by the electrical discharges. (This 

 paper will appear in full in the Journal of Ter- 

 restrial Magnetism for December, 1910.) 



Recent Work on the Selective Emission of the 

 Welsbach Mantle and the Acetylene Flame: 

 Dr. W. W. COBLENTZ, of the Bureau of 

 Standards. 



The speaker described experiments on the emis- 

 sion and the absorption of the acetylene flame. 

 The results obtained show that, within the limits 

 of experimental error, in the visible spectrum the 

 emissivity is a simple function of the thickness 

 of the radiating layer of the flame, while in the 

 infra-red tlie emissivity is a more complex func- 

 tion of the thickness. The acetylene flame has an 

 absorption band at .6 jx, with regions of greater 

 transparency in the violet and in the red. No 

 emission band exists at .7 fj., as was previously 

 supposed. The conclusion reached is that the 

 radiation from the acetylene flame is purely ther- 

 mal, and that it is not necessary to introduce the 

 question of luminescence to explain the observa- 

 tions. 



Experiments were also described on the radia- 

 tion from the Welsbach mantle and from the 

 same material used as a solid rod. The spectral 

 energy curves of these two forms of radiators of 

 the same material are entirely different, due to 

 the difference in the thickness of the radiating 

 layer. Cerium oxide changes its pigment color 



