safford: lignum nephriticum 517 



SUMMARY 



Lignum nephriticum mexicanum, a wood remarkable for the 

 blue fluorescence of its infusion in spring water, was celebrated 

 throughout Europe in the 16th century as a diuretic. Its 

 botanical identity has remained uncertain until the present time. 



It proves to be the wood of a leguminous tree, Eysenhardtia 

 polystachya occupying an exensiVe range in the interior of Mexico. 

 The botanical description of the tree corresponds well with that 

 of Hernandez written in the 16th century. Its pinnately com- 

 pound leaves bear a general resemblance to those of Cicer arieti- 

 nuin and also suggest the divided leaves of Ruta chalepensis. Its 

 small flowers, arranged in spicate clusters, though white when 

 fresh, soon turn j-ellow in dried specimens. Its wood, straight- 

 grained and dense and free from knots, yields a tincture in spring- 

 water (containing a slight percentage of lime) which shows a 

 remarkable blue fluorescence and in an opaque vessel appears 

 quite blue. 



Its botanical identity remained uncertain for so long a time 

 owing to the following causes: (1) Commercial specimens of the 

 wood were unaccompanied by botanical material; (2) botanical 

 material in herbaria was lacking in wood ; (3) the phenomenon 

 of fluorescence as seen in ordinary dayhght is produced by an 

 infusion of the dark-colored heartwood, while the light-colored 

 sapwood of stems and of moderate-sized branches, though 

 yielding a fluorescent infusion as seen in ultra-violet rays, does 

 not yield a fluorescence perceptible in daylight ; (4) the plant was 

 first described from a shrub in all probability too young to possess 

 heartwood, and the author of the species was unaware of its 

 identity with lignum nephriticum or even of its power to produce 

 the phenomenon of fluorescence. 



For the first time the botanical identity of the true lignum 

 nephriticum mexicanum has been established beyond a doubt, 

 bj^ the study and exhibition of specimens of wood corresponding 

 accurately with the descriptions of Robert Boyle, yielding the 

 characteristic fluorescence obtained by him in his experiments, 

 and accompanied by botanical specimens from the tree producing 

 the wood, these agreeing in all respects with the original descrip- 

 tion by Hernandez of the plant yielding lignum nephriticum. 



