The Development and Germination of the Intraepidermal Teliospores of Melampsorella Cerastii

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Abstract
The teliospores of Melampsorella cerastii are developed in the lower epidermis of the young leaves of Cerastium arvense in the spring from a systemic perennial mycelium. Hyphae mass up above the cells of the lower epidermis and from certain hyphal cells of the fungus enlarged binucleate primordial cells are formed. Each primordial cell penetrates the host cell wall and the contents flow in to form a teliospore initial which, by growth and differentiation, develops directly into a single-celled thin-walled teliospore. Following nuclear fusion the teliospore immediately germinates, producing a slender recurved promycelium into which the fusion nucleus migrates. Meiosis occurs here and four uninucleate basidiospores are produced. Teliospores completely fill all of the cells of the lower epidermis of the lower leaves, giving the leaf an orange color. Some teliospores are formed in the middle leaves but are lacking in the upper leaves. Teliospore formation is continuous during the first few weeks and new initials are formed in the cells as the teliospores germinate. Comparisons were made with the other rust species with intraepidermal teliospores which have been examined cytologically. Melampsorella cerastii is similar in its general development but differs principally in that the teliospore is unicellular.