SAPROPHYTISM. 23 



But the ferns were the most abundant both in kinds and indi- 

 viduals, since fully one-half of the known Carboniferous plants belong 

 to this class. They were so numerous that in some places layers of 

 coal were built up almost entirely of their microscopic spores and 

 spore-cases. 



SAPROPHYTISM.* 

 By Dr. D. T. MacDougal. 



THE dictum of Liebig's time that humus and organic substances 

 in soil are of no use to green plants except so far as they 

 modify the physical characteristics of the sub-stratum, has been 

 found untenable long since. Several years ago it was deter- 

 mined that urea, glycocoU, uric acid, leucin, and tyrosin might be 

 available as food-substances for green plants. 



Within the last three years Leow and Bokorny have extended 

 this list to include forty organic compounds, such as methyl alcohol, 

 phenol, trimethylamin, skatol, and lecithin in addition to those given 

 above. Of the list of substances named by these investigators, leucin, 

 tyrosin, skatol, amides, amido-acids, formic acid, acetic acid, and 

 propionic acid result from the decomposition processes of humus and 

 are generally present in such soils in appreciable quantity. Recently 

 Jules Laurent has shown that the roots of maize are capable of ab- 

 sorbing complex substances as glucose and invert sugar at a rate cor- 

 responding exactly to the bulk of the plant body. The sugars ab- 

 sorbed are used, as is demonstrated by the increase in weight and by 

 the amount of carbon dioxide exhaled. Exact cultural experiments 

 with such aquatic species as Lemna, Spirogyra, Vaucheria^ and other 

 Algae have proven that these organisms thrive better in media con- 

 taining organic compounds and that this is due to the absorption of 

 some of these substances. Boulhac has shown that Nostoc puncti- 

 forme is capable of using glucose as a food-substance, which is in 

 harmony with the previous results obtained. Then again it has been 

 determined that plants furnished with nitrogen in the form of aspara- 

 gin show a better growth and a more ready acquisition of this import- 

 ant element, than when it is furnished in the form of nitrates. 



Given, then, the fact that green plants of greatly different physiolo- 

 gical constitution may absorb and use organic substances occurring in 

 the sub-stratum or liquid medium, and that a better nutrition results 

 from the presence of these substances, it is but fair to conclude that 



*Note from an abstract read before the Botanical Society of America, Boston, August 20, 



