Development of Spore-Forms and the Nuclear Cycle in the Autoecious opsis Rust, Cystopsora oleae

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Abstract
Cystopsora oleae* has both 2-and 4-celled promycelia. The rust is an autoecious opsis form and causes hypertrophy and witches" brooms on young leaves and twigs. Infection patches on which telia are formed, however, are not malformed. Teliospores germinate in situ without a rest period. Young teliospores are binucleate. Fusion takes place in mature spores. Promy-celium is formed by the extension of the lower part of the teliospore, and the syncaryon moves into it and divides twice. If the promycelium is 4-celled the cells are uni-nucleate but are binucleate if it is 2-celled. The sporidia are always binucleate. The binucleate condition persists so far as it has been possible to determine, and it is pre-sumed that the diplophase is initiated within the sporidium itself. The pycnium is thus borne on a diploid thallus, as all the associated mycelium has a pair of conjugate nuclei in each cell, although the pycniospores are uninucleate. Formation of aeciospores within the pycnia has been observed many times. When aeciospores are sown on young leaves, they invariably give rise to pycnia, although they have never been observed to form promycelia and sporidia. When older leaves are infected, teliospore development takes place, but after a lapse of several weeks. This rust thus presents certain remarkable characteristics not previously observed among other rusts and appears to be a form in very unstable condition.[long dash]The diagnostic characters of the genus and sp. are emended.