[Vol. 10 



302 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



Lutz ('05), using a modified Raulin's solution as the basis of a 

 culture medium, compared the assimilability by Aspergillus 

 niger of NH« salts, amines, amides, and nitriles by obtaining dry 

 weights of the felts for a given period of incubation. He con- 

 cluded that amides were the most assimilable, exceeding the 

 NH« salts; amines came next, and the order of their assimilability 

 was in inverse ratio to the size of their molecule; while nitriles 

 were of little value. He stated: "This conclusion is in perfect 

 concordance with that which we know of the chemical con- 

 stitution of these diverse bodies; those in which the molecule is 

 the more simple theoretically ought to be and practically are 

 the better source of N for the plants." 



Ritter ('09) worked with 8 different fungi, and employed, as 

 criteria, dry weight and the quantity of 0.1 N alkali required 

 to neutralize 10 ml. of the culture fluid after growth of the 

 organisms. He formulated the following conclusions: (1) The 

 weaker and less poisonous the free acids the better NH« is taken 

 up out of its mineral salts. (2) The development of fungi on 

 NH«-salt solutions is in direct proportion to their ability to with- 

 stand free acid. (3) In relation to the quantity of mineral acids 

 they are capable of generating, the fungi are placed in 2 groups: 

 (a) the mat-forming fungi, as Aspergillus and Rhizopus, which 

 liberate more acid than would permit the germination of their 

 spores, and (b) such fungi as various species of Mucor, which 

 grow submerged and produce acid in concentration not in- 

 hibitive to spore germination. (4) Aspergillus glaucus, Mucor 

 racemosus, and Cladosporium herbarum, designated "Nitratpilze," 

 develop as well on ammonium (NH<).N. (5) These 3 fungi, 

 however, show a strongly evident capacity for NO a assimilation; 

 Aspergillus niger, Botrytis cinerea, and Penicillium spp. are weaker 

 in this capacity and produce greater growth on (NH 4 ),SO<; 

 a third group, represented by Rhizopus nigricans, Mucor Mucedo, 

 and Thamnidium elegans refuse nitrates. 



In the 1912 paper he continues his ('09) observations, here 

 employing other carbon sources than the grape sugar of the former 

 work. By an ingenious method of draining the culture fluid off 

 the mat and flooding the fungus with an alkaline nitrate solution, 

 then incubating 2 or 3 days, he demonstrated the significant re- 



