SUMMARYThe effects of abscisic acid (ABA) and its interaction with gibbereOic acid (GA), indoleacetic acid (IAA) and kinetin on the germination of spores and growth of protonemata of the fern, Mohria caffrorum Sw. -were studied. ABA did not affect the initial divisions of the spore protoplast leading to the formation of rhizoid and protonenna, but inhibited the subsequent elongation of the latter. The apparent reversal of ABA-induced inhibition of protonemal elongation by GA appears to be due to an overall growth promotion by GA,. rather than due to its interaction -with ABA. On the other hand, both IAA and kinetin, which by themselves did not promote protonemal gro-wth, reversed to some extent the inhibitory effect of ABA on the growth of the protoneniia.