Apr. 7,1923 
Temperature Relations of Eleven Species of Rhizopus 39 
must be kept in mind, however, that other species may be destructive 
at temperatures which are not favorable for the development of nigricans y 
although at the present time little is known regarding the distribution 
and destructiveness of the other species under natural conditions in 
the United States. 
SUMMARY 
(1) The effect of temperatures on the spore germination, mycelial 
growth, and fruiting of ii species of Rhizopus has been studied, and the 
results are presented in this paper. 
(2) These ii species fall into three groups as regards their response 
to temperature. Chinensis has a temperature maximum and optimum 
several degrees higher than any of the other species and hence can be 
easily separated from them; nigricansy microsporusy reflexuSy and artocarpi 
make up a group having a low optimum and maximum; while the 6 
remaining species, namely, tritici, nodosusy delemary oryzacy arrhizuSy 
and maydis constitute an intermediate group. 
(3) In general the spores will germinate at a temperature above the 
maximum for continued growth. 
(4) The optimum for germination for all the species is higher than for 
growth and fruiting, while in most cases the optimum for fruiting is 
about the same as for growth. 
(5) The temperature at which the spores are produced influences to 
some extent their rate of germination and the early period of the growth 
of the mycelium developed therefrom. Spores of nigricans produced 
at 10° C. germinated in 30 minutes less time than those formed at 20° 
and 26°. Spores of this species from different cultures grown under 
like conditions germinated equally well, regardless of age, up to 20 days. 
(6) Spores of nigricans germinate in a considerably shorter time in a 
nutrient solution than in water. Sweet potato decoction proved to be 
the best liquid and string bean agar the best solid medium tried. In 
the comparative tests made this fungus grew nearly twice as fast on 
string bean agar as on Irish potato agar. 
(7) The presence of 20 per cent dextrose in Irish potato agar changed 
the cardinal temperatures of the strain of nigricans studied from i 
to 2^ C. 
(8) Nigricans y which seems to be the most destructive member of this 
genus, under natural conditions is somewhat limited in its field of destruc¬ 
tion by temperature. The spores were invariably killed at 35° C., and 
growth was very sparse and slow at 6.5°. At 1.5° no appreciable growth 
was made, on Irish potato agar in 30 days. 
LITERATURE CITED 
(1) Ames, Adeline. 
1915. THE TEMPERATURE RELATIONS OP SOME PUNGI CAUSING STORAGE ROTS. 
In Phytopathology, v. 5, p. 11-19. Bibliographical footnotes. 
(2) Anderson, P. J. 
1918. rose canker AND ITS CONTROL. Mass. Agf. Exp. Sta. Bui. 183, p.11-46, 
II fig., 3 pi. Literature cited, p. 46. 
(3) BruderlEin, J. 
1917. LE rhizopus maydis, n. sp. In Bui. Soc. Bot. Geneve, s6r. 2, v. 9, 
p. 108-112. 
(4) Doran, William L. 
1919. THE MINIMUM, OPTIMUM, AND MAXIMUM TEMPERATURES OP SPORE GERMI¬ 
NATION IN SOME UREDINALES. In Phytopathology, v. 9, p. 391-402. 
Literature cited, p. 401-402. 
