1905] BLAKESLEE—CONIDIA-BEARING FUNGI 163 
which it had been shown, by the production of their zygospores, that 
the two opposite strains were present together. By a sufficient 
accumulation of material from different sources one may expect 
eventually to obtain the two sexual strains, and by their synthesis 
the zygospores as well of those forms in which the sexes are separate 
on different mycelia. 
Cunninghamella, although reported by only two previous investi- 
gators, is not extremely rare. ATKINSON writes that he has had the 
species in cultures several times, and it has appeared occasionally in 
the Harvard laboratory, especially on material from the tropics. A 
pure culture of the fungus was thus obtained from dried flowers col- 
lected by the writer in Venezuela, and when contrasted in a culture 
between the (+) and (—) strains of a test species was shown to be 
(+) in character by the formation of imperfect hybrids with the (—) 
strain tested (J. c. pl. 2. figs. 36-39). Later a culture was secured from 
Porto Rico, and upon being similarly tested proved to be (—). The 
(+) and (-) strains thus determined were at once mutually con- 
trasted and, as was to be expected, yielded an abundant production 
of zygospores. These cultures were made at laboratory tempera- 
ture during warm weather in the latter part of July. In the fall the 
experiment was repeated; but although the two (+) and (—) strains 
separately continued to produce imperfect hybrids with (—) and (+) 
test strains respectively, yet when under the same cultural conditions 
contrasts were made between the two strains themselves no zygo- 
spores resulted. A series of cultures under various external condi- 
tions demonstrated that with this species the temperature is one of 
the most important factors to be considered in securing a formation 
of zygospores. At 20° C. zygospores have not been obtained; but at 
temperatures from 25° to 34° inclusive, zygospores readily form on 
the usual culture media employed in the laboratory. It is certainly 
remarkable that under any conditions the sexual response should be 
less intense when the (+) and (—) strains of a given species are con- 
trasted together than when they are contrasted against strains of a 
ferent species, but Cunninghamella is not unique in this respect. 
A like condition has already been noted in a species of the genus 
Mucor (/. c. 308, diagram), and a number of other forms more recently 
vestigated show a similar behavior. 
