468 pittier: caesalpiniaceous trees of panama 



tion is no doubt a close approximation to the actual mineral com- 

 position. The composition of the norm is given for comparison. 



Mode and norm of nepheline basalt from about 24 miles east of Blackfoot, Idaho 



Mode Norm Difference 



Apatite 1 1 



Ilmenite 1 1 



Magnetite 3 5 2 



Biotite 8 -S 



Forsterite 26 31 5 



Diopside 39 25 -14 



Xepheline 20 11 -9 



Orthoclase 9 9 



Albite 6 6 



Anorthite 9 9 



H2O 2 2 



Total 100 100 



The comparison of the norm and the mode thus indicates that 

 the norm shows more magnetite, forsterite, and feldspar than the 

 mode and less biotite, diopside, and nepheline. 



BOTANY. — Some new caesalpiniaceous trees of Panama. Henry 

 Pittier, Bureau of Plant Industry. 



The botanical exploration of the Isthmus of Panama begun 

 under the auspices of the Smithsonian Institution in 1910, and 

 since continued occasionally, has brought to light startling facts 

 with reference to the occurrence of certain genera hitherto un- 

 known within that region. It has been known for a long time 

 that Middle America is mainly a territory of transition between 

 the floras of two continents, in which many genera have their 

 northernmost or southernmost limit, the proportion of either 

 South American or North American species respectively decreas- 

 ing or increasing according to the distance from their centers of 

 dispersion. But there was no indication whatever of the very 

 sudden change which takes place in Darien, the eastern part of 

 Panama and the connecting link with South America. 



