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Abstract
SUMMARY: Colonies of Rhizopus sexualis (Smith) Callen on 1 % (w/v) malt agar at 20° show the first stages in conjugation approximately 40 hr. after inoculation and the first mature zygospores after a further 32–34 hr. Transfer to 5–10° prevents the initiation of conjugation and inhibits the further development of the majority of pairings in which the gametangia are not fully delimited at the time of transfer. Fully delimited gametangia continue to develop and to produce mature zygospores at the low temperature. This effect is almost entirely independent of the composition and pH value of the medium. Sporangia are produced in greater numbers at the low temperature than at 20°. The effect of low temperature on formation of zygospores of Mucor hiemalis, Zygorrhynchus macrocarpus and Z. moelleri is essentially similar to that with R. sexualis, but Phycomyces blakesleeanus shows only slight inhibition at 5° and none at 7° or over. The significance of the inhibitory effect is discussed.
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