280 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



I. Mexican Lignum Nephriticum. 



Eysenhardtia jyolystachya. 



In connection with his work on the economic botany of Mexico the 

 writer has for years been seeking the source of lignum nephriticum. 

 Among other woods examined for the blue fluorescence characterizing 

 this wood were specimens of branches of EysenJiarcUia polystachya 

 collected by the writer in 1907 in the vicinity of Aguascalienthes, the 

 infusion of which gave no evidence of fluorescence in ordinary sun- 

 light. From this fact and from the fact that all specimens seen by 

 him were either shrubs or trees too small to yield wood for the 

 manufacture of bowls or cups, the writer was inclined to agree with 

 MoUer in discarding Eysenhardtia as a possible source of the famous 

 wood. In July, 1914, however, specimens of a medicinal wood from 

 Mexico were brought to the writer accompanied by herbarium mate- 

 rial from the same tree. It proved to be Eysenhardtia polystachya^ 

 known by the modern Mexicans in many localities as palo didce^ or 

 " sweet wood." Its collector had not noticed anything peculiar about 

 the color of its infusion, but dwelt upon its efficacy as a cure for 

 certain diseases to which fowls are subject in Mexico. The wood was 

 a section of a tree trunk, which deprived of its bark was 7 cm. in 

 diameter, and which, unlike all specimens of Eysenhardtia wood 

 hitherto seen by- the writer, consisted chiefly of dense, straight-grained 

 dark brown heartwood very much like lignum-vitse {Guaia.cu7n 

 offimmile) in appearance, surrounded by a ring of brownish-white 

 sapwood 5 to 8 mm. thick. A few small chips of the heartwood in 

 ordinary tap water tinged the latter a golden yellow, which soon 

 deepened to orange and appeared like amber when held between the 

 e5^e and window. When the glass vial containing the liquid was held 

 against a dark background the liquid glowed with a beautiful peacock 

 fluorescence very much like that seen in quinine. Placed partly in 

 a sunbeam half of the liquid appeared j^ellow and the other half 

 blue; and when the sunlight was focused upon it by the lens of a 

 common reading glass, the vial appeared to be filled with radiant 

 gold penetrated by a shaft of pure cobalt. There was no longer any 

 doubt as to the identity of the wood. It could only be the Mexican 

 lignufti nephriticum of Robert Boyle's experiments, and it was un- 

 doubtedly the wood of Eysenhardtia polystachya^ a tree with small 

 pinnately compound leaves which might indeed suggest those of a 

 chick-pea or of the common wild rue of Spain, and with spikes of 

 small flowers which had turned yellowish in drying, corresponding 

 well with Hernandez's description of the coatl of the Aztecs. 



Plate 3 shows a photograph of a section of the wood of Eysen- 

 hardtia polystachya together with the botanical material which 

 served to identify it. 



