C. II. White — Autophytography . 233 



received a black deposit on their polished and stained surfaces, 

 reproducing so perfectly the stem and leaves of a small herb 

 that the species is readily identified. These autophytographs 

 were determined by Mr. M. L. Fernald at the Gray Herba- 

 rium, Harvard University, through the kind intervention of 

 Mr. Walter Dearie, of Cambridge, Massachusetts, as having 

 been produced by Micranthemum orhiculatum Michx., a 

 small creeper that flourishes in low, muddy ground, from 

 Florida to North Carolina. 



The composition of the pigment of these antophytographs is 

 difficult to determine, owing to the small quantity of material 

 available. It is, however, a black adherent deposit, insoluble 



in water, but slowly attacked by the mineral acids, yielding 

 solutions which show the presence of iron. No change of 

 color is produced by the flame of the blow-pipe, but the pig- 

 ment becomes strongly magnetic on heating. There is no 

 doubt, therefore, that the colored deposit contains iron, and it 

 is most probably an oxide. Two possible conditions under 

 which it is believed such a deposit could form are suggested. 

 First, the plants of this genus may yield on decomposition a 

 precipitant of iron, peculiar to the genus, which extracts iron 

 from the surrounding solutions and deposits it in a manner 

 analogous to one of the artificial ink-making processes, and on 

 exposure to the air the precipitate is changed to an oxide. 

 The other suggestion is, that the conditions of decay are such 

 that ammonia is liberated in the presence of iron in solution, 

 precipitating the iron on the rock upon which the j)lant rests 



