218 PROCEEDINGS OF THE AMERICAN ACADEMY. 



a culture beginning to form zygospores by a change to any one of a number 

 of unfavorable conditions. 



lu marked contrast to the results of Klebs, Falck ('01) finds that, 

 within normal limits, relative humidity of the air and transpiration have 

 no influence in determining the form of fructification. He denies Klebs' 

 assumption that the hyphae bearing sporangia, and those bearing zygos- 

 pores, are morphologically equivalent, and shows that the zygospores do 

 not result from the meeting of adjacent outgrowths, but that these out- 

 growths arise through the stimulation of contact of neighboring hyphae, 

 and are never separate. Falck concludes that with sufficient nutriment 

 the concentration is the special condition effective for zygospore forma- 

 tion. Starting with a normal nutrient solution by the addition of in- 

 creasing amounts of grape sugar, peptone, glycerine, or mineral salts, 

 a gradual change can be induced from a condition in which sporangia 

 alone are produced, to one in which zygosporic reproduction predominates. 

 Concentration of a normal solution will bring on zygospore production, 

 while if a solution already producing zygospores is sufficiently diluted, 

 sporangia only are formed. When carbohydrates predominate in the 

 nutrient, the harvest depends on the amount of peptone, while the reverse 

 is true when peptone predominates. In the former case the zygospores 

 are black and relatively poor in protein, while in the latter they are 

 brown and the protein per cent is higher. 



The publication of the results obtained by Falck led Klebs to test 

 again the effects of relative humidity and transpiration, and in a second 

 paper ('02) he confirms his former conclusion that the appearance of 

 zygospores or of sporangia in different cases depends chiefly on the 

 amount of transpiration, and that the concentration is of secondary im- 

 portance. He suggests that the opposite results of Falck were due to 

 his working with a different race. That such physiologically different 

 strains of Sporodinia do exist is shown by. Falck's (1. c, p. 300) dis- 

 covery of a form which produced zygospores even in dilute solutions, 

 and would seem therefore to be more like the strain used by Klebs. 



It is evident that the conclusions above enumerated are diverse and con- 

 flicting to a marked degree. While one author demands excess of 

 moisture or of oxygen as a crucial factor, another postulates conditions 

 exactly the reverse. The seeker for zygospores may choose between 

 an abundant food supply or a substratum poor in nutriment. The 

 presence of parasites is held by one writer to produce, by another to 

 inhibit, zygospore formation. As has already been suggested, the lack 

 of agreement among the results of different investigators is, in the 



