. The fungi which cause plant disease . Plant diseases; Fungi. 172 THE FUNGI WHICH CAUSE PLANT DISEASE formed at once and the mycelium develops to a more or less circular colony, producing new conidia in a few days. Artificial inoculations on susceptible plants, using conidia, usually result within two to five days in typical mildew spots. Neger,*" who studied the germination of conidia extensively has shown that light hastens the growth of the germ tubes, which in many cases are negatively phototropic. Con- tact stimulus leads to the growth of appres- soria. The perithecia are subspheric
. The fungi which cause plant disease . Plant diseases; Fungi. 172 THE FUNGI WHICH CAUSE PLANT DISEASE formed at once and the mycelium develops to a more or less circular colony, producing new conidia in a few days. Artificial inoculations on susceptible plants, using conidia, usually result within two to five days in typical mildew spots. Neger,*" who studied the germination of conidia extensively has shown that light hastens the growth of the germ tubes, which in many cases are negatively phototropic. Con- tact stimulus leads to the growth of appres- soria. The perithecia are subspherical, often some- _ what flattened, white to yellow when young, showing lobed haus^ dark to black and reticulated when mature; toria. After Salmon. ^^^ ^thout ostiolc but are provided with appendages of various types. Figs. 130, 133-136, which give main characters to mark the genera. The appendages serve by hygro- scopic movements to aid in the distribution of the fungus.*^ The ascospores become free after dissolution of the perithecium by weathering. The asci are either solitary or quite numerous within the perithecium and bear two to eight hyaline spores each. The conidia are short-lived summer spores. The perithecia mature more slowly and constitute the hibernating condition. In some instances the ascus-form is unknown; the fungus is then classified solely by its conidial stage and falls under the form genus Oidium (see p. 569.) In Sphserotheca *'' an antheridial and an oogonidial branch, each uninucleate, are de- veloped, and cut off by septa. The oogo- nium enlarges; the antheridium lengthens, fig. i24.^AZ^nium- its nucleus divides, and a septum is run in *"'^ '^^ ^™ nuclei, separating the stalk cell from the antheri- ^^ "^"' dium. The sperm nucleus enters the oogonium and fuses with the oogonial nucleus. Simultaneous with fertilization oc- curs, from the stalk cell of the oogonium, the development of a sterile system of enveloping threads which surround and
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfungi, bookyear1913
