. A textbook of botany for colleges and universities ... Botany. THALLOPHYTES 65 Jmigus that has retained swimming sperms. â These sperms are uniciliate, as are the zoospores,, a fact which suggested the generic name. Peronosporales. â âThese are the downy mildews, and they include many destructive parasites that live within the tissues of the host, the hyphae branching through the intercellular spaces, crowding between the cells, and sending haustoria into them. This internal mycelium sends sporophores to the surface of the host, and spores are formed by round- ing off the tips of the sporoph
. A textbook of botany for colleges and universities ... Botany. THALLOPHYTES 65 Jmigus that has retained swimming sperms. â These sperms are uniciliate, as are the zoospores,, a fact which suggested the generic name. Peronosporales. â âThese are the downy mildews, and they include many destructive parasites that live within the tissues of the host, the hyphae branching through the intercellular spaces, crowding between the cells, and sending haustoria into them. This internal mycelium sends sporophores to the surface of the host, and spores are formed by round- ing off the tips of the sporophores or their branches. This process of cutting off spores is called abstriction, and such spores are called conidia. Oogonia and antheridia are formed upon the internal mycelium, and fertilization is effected through a fertilizing tube. This is the one group of Oomy- cetes with distinctly aerial habit, as in the Zygomycetes ; but the forms are heterogamous, and in the life history of many of them zoospores appear. The promi- nent genera are as follows: Albugo. â A. Candida is the white rust which attacks mem- bers of the mustard family, causing distortions, especially in the flower clusters. The myce- lium traverses the intercellular spaces of the host, the haustoria sent into the host cells being slender branches which enlarge at the ends into little knobs. The sporophores arise in clusters and press up the epidermis, which then appears like a white blister (fig. 158). Finally the epidermis is broken and the sporophores are ^ ^â ,.,,,. : . Fig. 158. â Albugo Candida (white rust); exposed, each endmg m a cham showing mycelium crowding among host cells of spores (conidia), which have and sending into them small button-like been formed by successive ab- haustoria, sporophores arising under epidermis ^ and abstricting multinucleate conidia (spores), Strictions of the sporophore. The ^^^ j^e detached and dying epidermis.â conidia are multinucleate, and After P
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
