. A textbook of botany for colleges and universities ... Botany. 66 MORPHOLOGY. upon germination produce numerous laterally biciliate zoospores. The zoospores germinate promptly, each one sending out a tube that penetrates the seedhng host and starts a new internal mycelium. The sex organs of this genus are formed on the deep mycelium, the oogonia and antheridia appearing on separate hyphae. The oogonium is a globular, multinucleate cell. In the organization of the egg, the protoplast is diflterentiated into a peripheral zone of cytoplasm (peri- plasm), which contains all the nuclei except one
. A textbook of botany for colleges and universities ... Botany. 66 MORPHOLOGY. upon germination produce numerous laterally biciliate zoospores. The zoospores germinate promptly, each one sending out a tube that penetrates the seedhng host and starts a new internal mycelium. The sex organs of this genus are formed on the deep mycelium, the oogonia and antheridia appearing on separate hyphae. The oogonium is a globular, multinucleate cell. In the organization of the egg, the protoplast is diflterentiated into a peripheral zone of cytoplasm (peri- plasm), which contains all the nuclei except one, and a central mass of cyto- plasm (ooplasm) containing a soli- tary nucleus for fertilization (fig. 159). The anthe- ridium is also a multinucleate cell (fig. 160), which sends out a fer- tilizing tube that reaches the egg, and through this the male nuclei are discharged. One male nucleus fuses with the solitary nucleus of the ooplasm, and a heavy-walled oospore is formed. The oospore is liberated by the decay of the surrounding host tissue, and on germination either produces zoospores or develops a mycelium directly. In certain other species (A. Bliti and A. Porlulacae), the numerous nuclei of the egg remain distributed throughout its mass (fig. 160), and when the male nuclei are discharged, there is multinucleate fusion, many nuclei pairing and fusing. Phytophthora. — P. infestans is the fungus producing potato rot, a disease of great economic importance. The mycelium vegetates in the green parts of the plant, causing wilting and withering of leaves and stem. The sporophores are sent to the surface in immense numbers through stomata, and branch, bearing solitary conidia on the branches. Damp, windy weather is said to spread the disease like wildfire. The mycelium winters in the tubers. Plasmopara. — P. viticola is the grape mildew, the groups of branching sporo- phores appearing like downy spots upon the surface of the host (conspicuous on the leaves.) The conidia upon
Size: 2330px × 1072px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
